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 $56.68   8.485%   $61.4893   $61.49   $61.50   $61.50  
  Purchase #2 $111.54   11.736%   $124.6303   $124.63   $124.65   $124.60  
  Purchase #3 $44.85   12.572%   $50.4885   $50.49   $50.50   $50.50  
  Purchase #4 $186.86   8.629%   $202.9841   $202.98   $203.00   $203.00  
  Purchase #5 $52.58   6.207%   $55.8436   $55.84   $55.85   $55.80  
  Purchase #6 $40.38   8.785%   $43.9274   $43.93   $43.95   $43.90  
  Purchase #7 $224.76   5.142%   $236.3172   $236.32   $236.30   $236.30  
  7 purchase totals = $717.65       $775.6804   $775.68   $775.75   $775.60