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 $250.67   5.788%   $265.1788   $265.18   $265.20   $265.20  
  Purchase #2 $177.87   8.580%   $193.1312   $193.13   $193.15   $193.10  
  Purchase #3 $59.54   3.502%   $61.6251   $61.63   $61.65   $61.60  
  Purchase #4 $201.51   11.487%   $224.6575   $224.66   $224.65   $224.70  
  Purchase #5 $61.54   3.201%   $63.5099   $63.51   $63.50   $63.50  
  Purchase #6 $67.40   11.514%   $75.1604   $75.16   $75.15   $75.20  
  Purchase #7 $129.70   7.739%   $139.7375   $139.74   $139.75   $139.70  
  7 purchase totals = $948.23       $1,023.0004   $1,023.01   $1,023.05   $1,023.00