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 $157.98   9.726%   $173.3451   $173.35   $173.35   $173.30  
  Purchase #2 $203.42   3.459%   $210.4563   $210.46   $210.45   $210.50  
  Purchase #3 $55.28   9.545%   $60.5565   $60.56   $60.55   $60.60  
  Purchase #4 $227.44   12.670%   $256.2566   $256.26   $256.25   $256.30  
  Purchase #5 $181.38   13.856%   $206.512   $206.51   $206.50   $206.50  
  Purchase #6 $209.82   4.117%   $218.4583   $218.46   $218.45   $218.50  
  Purchase #7 $85.82   8.849%   $93.4142   $93.41   $93.40   $93.40  
  7 purchase totals = $1,121.14       $1,218.9990   $1,219.01   $1,218.95   $1,219.10