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 $55.71   9.217%   $60.8448   $60.84   $60.85   $60.80  
  Purchase #2 $132.73   11.383%   $147.8387   $147.84   $147.85   $147.80  
  Purchase #3 $54.59   9.422%   $59.7335   $59.73   $59.75   $59.70  
  Purchase #4 $201.46   13.602%   $228.8626   $228.86   $228.85   $228.90  
  Purchase #5 $248.51   5.142%   $261.2884   $261.29   $261.30   $261.30  
  Purchase #6 $221.77   10.233%   $244.4637   $244.46   $244.45   $244.50  
  Purchase #7 $210.47   12.288%   $236.3326   $236.33   $236.35   $236.30  
  7 purchase totals = $1,125.24       $1,239.3643   $1,239.35   $1,239.40   $1,239.30