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 $46.75   11.731%   $52.2342   $52.23   $52.25   $52.20  
  Purchase #2 $75.30   3.592%   $78.0048   $78.00   $78.00   $78.00  
  Purchase #3 $149.69   10.356%   $165.1919   $165.19   $165.20   $165.20  
  Purchase #4 $80.51   13.397%   $91.2959   $91.30   $91.30   $91.30  
  Purchase #5 $155.76   8.544%   $169.0681   $169.07   $169.05   $169.10  
  Purchase #6 $203.88   5.134%   $214.3472   $214.35   $214.35   $214.30  
  Purchase #7 $163.69   11.290%   $182.1706   $182.17   $182.15   $182.20  
  7 purchase totals = $875.58       $952.3127   $952.31   $952.30   $952.30