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 $181.47   9.454%   $198.6262   $198.63   $198.65   $198.60  
  Purchase #2 $160.87   13.662%   $182.8481   $182.85   $182.85   $182.80  
  Purchase #3 $121.29   12.183%   $136.0668   $136.07   $136.05   $136.10  
  Purchase #4 $68.40   4.767%   $71.6606   $71.66   $71.65   $71.70  
  Purchase #5 $184.67   10.341%   $203.7667   $203.77   $203.75   $203.80  
  Purchase #6 $166.99   9.495%   $182.8457   $182.85   $182.85   $182.80  
  Purchase #7 $157.67   10.592%   $174.3704   $174.37   $174.35   $174.40  
  7 purchase totals = $1,041.36       $1,150.1845   $1,150.20   $1,150.15   $1,150.20