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 $208.62   7.619%   $224.5148   $224.51   $224.50   $224.50  
  Purchase #2 $228.39   10.190%   $251.6629   $251.66   $251.65   $251.70  
  Purchase #3 $14.38   3.173%   $14.8363   $14.84   $14.85   $14.80  
  Purchase #4 $161.35   3.277%   $166.6374   $166.64   $166.65   $166.60  
  Purchase #5 $238.98   8.175%   $258.5166   $258.52   $258.50   $258.50  
  Purchase #6 $247.27   10.387%   $272.9539   $272.95   $272.95   $273.00  
  Purchase #7 $124.70   10.465%   $137.7499   $137.75   $137.75   $137.70  
  7 purchase totals = $1,223.69       $1,326.8718   $1,326.87   $1,326.85   $1,326.80