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 $168.87   8.233%   $182.7731   $182.77   $182.75   $182.80  
  Purchase #2 $133.54   11.103%   $148.3669   $148.37   $148.35   $148.40  
  Purchase #3 $227.52   13.407%   $258.0236   $258.02   $258.00   $258.00  
  Purchase #4 $233.31   5.535%   $246.2237   $246.22   $246.20   $246.20  
  Purchase #5 $220.76   3.602%   $228.7118   $228.71   $228.70   $228.70  
  Purchase #6 $244.52   7.735%   $263.4336   $263.43   $263.45   $263.40  
  Purchase #7 $28.32   7.779%   $30.523   $30.52   $30.50   $30.50  
  7 purchase totals = $1,256.84       $1,358.0557   $1,358.04   $1,357.95   $1,358.00