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 $137.74   10.781%   $152.5897   $152.59   $152.60   $152.60  
  Purchase #2 $130.41   3.767%   $135.3225   $135.32   $135.30   $135.30  
  Purchase #3 $189.74   9.428%   $207.6287   $207.63   $207.65   $207.60  
  Purchase #4 $141.62   3.226%   $146.1887   $146.19   $146.20   $146.20  
  Purchase #5 $154.38   10.242%   $170.1916   $170.19   $170.20   $170.20  
  Purchase #6 $58.37   6.259%   $62.0234   $62.02   $62.00   $62.00  
  Purchase #7 $173.36   4.276%   $180.7729   $180.77   $180.75   $180.80  
  7 purchase totals = $985.62       $1,054.7175   $1,054.71   $1,054.70   $1,054.70