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 $146.99   5.169%   $154.5879   $154.59   $154.60   $154.60  
  Purchase #2 $203.45   3.395%   $210.3571   $210.36   $210.35   $210.40  
  Purchase #3 $211.75   5.553%   $223.5085   $223.51   $223.50   $223.50  
  Purchase #4 $94.92   9.276%   $103.7248   $103.72   $103.70   $103.70  
  Purchase #5 $224.93   13.133%   $254.4701   $254.47   $254.45   $254.50  
  Purchase #6 $26.56   5.797%   $28.0997   $28.10   $28.10   $28.10  
  Purchase #7 $239.43   11.357%   $266.6221   $266.62   $266.60   $266.60  
  7 purchase totals = $1,148.03       $1,241.3702   $1,241.37   $1,241.30   $1,241.40