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 $218.25   13.112%   $246.8669   $246.87   $246.85   $246.90  
  Purchase #2 $65.55   5.742%   $69.3139   $69.31   $69.30   $69.30  
  Purchase #3 $212.35   11.838%   $237.488   $237.49   $237.50   $237.50  
  Purchase #4 $72.37   3.434%   $74.8552   $74.86   $74.85   $74.90  
  Purchase #5 $29.95   6.707%   $31.9587   $31.96   $31.95   $32.00  
  Purchase #6 $177.57   13.632%   $201.7763   $201.78   $201.80   $201.80  
  Purchase #7 $47.85   11.317%   $53.2652   $53.27   $53.25   $53.30  
  7 purchase totals = $823.89       $915.5242   $915.54   $915.50   $915.70