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 $56.88   5.826%   $60.1938   $60.19   $60.20   $60.20  
  Purchase #2 $161.58   12.766%   $182.2073   $182.21   $182.20   $182.20  
  Purchase #3 $145.65   3.197%   $150.3064   $150.31   $150.30   $150.30  
  Purchase #4 $236.48   10.523%   $261.3648   $261.36   $261.35   $261.40  
  Purchase #5 $106.81   12.780%   $120.4603   $120.46   $120.45   $120.50  
  Purchase #6 $232.60   7.290%   $249.5565   $249.56   $249.55   $249.60  
  Purchase #7 $37.62   4.342%   $39.2535   $39.25   $39.25   $39.30  
  7 purchase totals = $977.62       $1,063.3426   $1,063.34   $1,063.30   $1,063.50