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 $224.43   8.392%   $243.2642   $243.26   $243.25   $243.30  
  Purchase #2 $58.55   4.728%   $61.3182   $61.32   $61.30   $61.30  
  Purchase #3 $157.89   7.107%   $169.1112   $169.11   $169.10   $169.10  
  Purchase #4 $182.47   13.359%   $206.8462   $206.85   $206.85   $206.80  
  Purchase #5 $94.99   8.266%   $102.8419   $102.84   $102.85   $102.80  
  Purchase #6 $113.85   12.330%   $127.8877   $127.89   $127.90   $127.90  
  Purchase #7 $69.66   4.770%   $72.9828   $72.98   $73.00   $73.00  
  7 purchase totals = $901.84       $984.2522   $984.25   $984.25   $984.20