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 $249.39   5.389%   $262.8296   $262.83   $262.85   $262.80  
  Purchase #2 $150.71   7.203%   $161.5656   $161.57   $161.55   $161.60  
  Purchase #3 $85.66   12.269%   $96.1696   $96.17   $96.15   $96.20  
  Purchase #4 $236.94   13.682%   $269.3581   $269.36   $269.35   $269.40  
  Purchase #5 $234.58   9.379%   $256.5813   $256.58   $256.60   $256.60  
  Purchase #6 $143.61   6.251%   $152.5871   $152.59   $152.60   $152.60  
  Purchase #7 $228.99   8.151%   $247.655   $247.66   $247.65   $247.70  
  7 purchase totals = $1,329.88       $1,446.7463   $1,446.76   $1,446.75   $1,446.90