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 $51.93   3.126%   $53.5533   $53.55   $53.55   $53.60  
  Purchase #2 $197.33   9.471%   $216.0191   $216.02   $216.00   $216.00  
  Purchase #3 $209.80   9.573%   $229.8842   $229.88   $229.90   $229.90  
  Purchase #4 $236.57   12.760%   $266.7563   $266.76   $266.75   $266.80  
  Purchase #5 $115.38   7.378%   $123.8927   $123.89   $123.90   $123.90  
  Purchase #6 $52.91   9.167%   $57.7603   $57.76   $57.75   $57.80  
  Purchase #7 $67.75   13.296%   $76.758   $76.76   $76.75   $76.80  
  7 purchase totals = $931.67       $1,024.6239   $1,024.62   $1,024.60   $1,024.80