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 $65.46   12.363%   $73.5528   $73.55   $73.55   $73.60  
  Purchase #2 $138.27   8.582%   $150.1363   $150.14   $150.15   $150.10  
  Purchase #3 $163.51   4.337%   $170.6014   $170.60   $170.60   $170.60  
  Purchase #4 $25.57   13.752%   $29.0864   $29.09   $29.10   $29.10  
  Purchase #5 $92.28   3.277%   $95.304   $95.30   $95.30   $95.30  
  Purchase #6 $97.39   11.195%   $108.2928   $108.29   $108.30   $108.30  
  Purchase #7 $154.91   3.262%   $159.9632   $159.96   $159.95   $160.00  
  7 purchase totals = $737.39       $786.9369   $786.93   $786.95   $787.00