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 $245.76   11.779%   $274.7081   $274.71   $274.70   $274.70  
  Purchase #2 $211.77   7.752%   $228.1864   $228.19   $228.20   $228.20  
  Purchase #3 $123.45   7.165%   $132.2952   $132.30   $132.30   $132.30  
  Purchase #4 $234.53   5.169%   $246.6529   $246.65   $246.65   $246.70  
  Purchase #5 $166.78   5.487%   $175.9312   $175.93   $175.95   $175.90  
  Purchase #6 $246.30   11.789%   $275.3363   $275.34   $275.35   $275.30  
  Purchase #7 $179.82   12.205%   $201.767   $201.77   $201.75   $201.80  
  7 purchase totals = $1,408.41       $1,534.8771   $1,534.89   $1,534.90   $1,534.90