Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $187.29   12.154%   $210.0532   $210.05   $210.05   $210.10  
  Purchase #2 $216.68   9.339%   $236.9157   $236.92   $236.90   $236.90  
  Purchase #3 $248.68   3.513%   $257.4161   $257.42   $257.40   $257.40  
  Purchase #4 $203.77   4.219%   $212.3671   $212.37   $212.35   $212.40  
  Purchase #5 $189.32   13.276%   $214.4541   $214.45   $214.45   $214.50  
  Purchase #6 $185.41   7.168%   $198.7002   $198.70   $198.70   $198.70  
  Purchase #7 $204.81   6.587%   $218.3008   $218.30   $218.30   $218.30  
  7 purchase totals = $1,435.96       $1,548.2072   $1,548.21   $1,548.15   $1,548.30