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 $227.32   5.276%   $239.3134   $239.31   $239.30   $239.30  
  Purchase #2 $244.55   3.401%   $252.8671   $252.87   $252.85   $252.90  
  Purchase #3 $29.76   10.532%   $32.8943   $32.89   $32.90   $32.90  
  Purchase #4 $58.63   6.633%   $62.5189   $62.52   $62.50   $62.50  
  Purchase #5 $201.90   4.238%   $210.4565   $210.46   $210.45   $210.50  
  Purchase #6 $123.45   13.837%   $140.5318   $140.53   $140.55   $140.50  
  Purchase #7 $179.85   4.309%   $187.5997   $187.60   $187.60   $187.60  
  7 purchase totals = $1,065.46       $1,126.1817   $1,126.18   $1,126.15   $1,126.20