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 $117.54   13.598%   $133.5231   $133.52   $133.50   $133.50  
  Purchase #2 $121.32   3.612%   $125.7021   $125.70   $125.70   $125.70  
  Purchase #3 $247.81   7.551%   $266.5221   $266.52   $266.50   $266.50  
  Purchase #4 $93.66   4.249%   $97.6396   $97.64   $97.65   $97.60  
  Purchase #5 $24.51   3.264%   $25.31   $25.31   $25.30   $25.30  
  Purchase #6 $235.68   8.688%   $256.1559   $256.16   $256.15   $256.20  
  Purchase #7 $20.53   3.768%   $21.3036   $21.30   $21.30   $21.30  
  7 purchase totals = $861.05       $926.1564   $926.15   $926.10   $926.10