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 $216.71   13.519%   $246.007   $246.01   $246.00   $246.00  
  Purchase #2 $156.73   8.293%   $169.7276   $169.73   $169.75   $169.70  
  Purchase #3 $162.96   7.432%   $175.0712   $175.07   $175.05   $175.10  
  Purchase #4 $8.46   11.653%   $9.4458   $9.45   $9.45   $9.40  
  Purchase #5 $87.34   9.147%   $95.329   $95.33   $95.35   $95.30  
  Purchase #6 $102.41   5.587%   $108.1316   $108.13   $108.15   $108.10  
  Purchase #7 $156.90   11.664%   $175.2008   $175.20   $175.20   $175.20  
  7 purchase totals = $891.51       $978.9130   $978.92   $978.95   $978.80