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 $208.84   11.676%   $233.2242   $233.22   $233.20   $233.20  
  Purchase #2 $214.61   9.220%   $234.397   $234.40   $234.40   $234.40  
  Purchase #3 $26.46   13.123%   $29.9323   $29.93   $29.95   $29.90  
  Purchase #4 $34.37   4.239%   $35.8269   $35.83   $35.85   $35.80  
  Purchase #5 $13.49   12.234%   $15.1404   $15.14   $15.15   $15.10  
  Purchase #6 $219.38   12.843%   $247.555   $247.56   $247.55   $247.60  
  Purchase #7 $148.85   11.360%   $165.7594   $165.76   $165.75   $165.80  
  7 purchase totals = $866.00       $961.8352   $961.84   $961.85   $961.80