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 $23.30   5.256%   $24.5246   $24.52   $24.50   $24.50  
  Purchase #2 $152.49   6.858%   $162.9478   $162.95   $162.95   $162.90  
  Purchase #3 $51.70   13.578%   $58.7198   $58.72   $58.70   $58.70  
  Purchase #4 $208.68   11.195%   $232.0417   $232.04   $232.05   $232.00  
  Purchase #5 $190.27   6.146%   $201.964   $201.96   $201.95   $202.00  
  Purchase #6 $233.60   9.654%   $256.1517   $256.15   $256.15   $256.20  
  Purchase #7 $17.94   12.577%   $20.1963   $20.20   $20.20   $20.20  
  7 purchase totals = $877.98       $956.5459   $956.54   $956.50   $956.50