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 $66.51   5.587%   $70.2259   $70.23   $70.25   $70.20  
  Purchase #2 $152.43   7.722%   $164.2006   $164.20   $164.20   $164.20  
  Purchase #3 $210.65   7.201%   $225.8189   $225.82   $225.80   $225.80  
  Purchase #4 $191.47   6.764%   $204.421   $204.42   $204.40   $204.40  
  Purchase #5 $236.76   8.371%   $256.5792   $256.58   $256.60   $256.60  
  Purchase #6 $160.73   13.376%   $182.2292   $182.23   $182.25   $182.20  
  Purchase #7 $100.52   12.180%   $112.7633   $112.76   $112.75   $112.80  
  7 purchase totals = $1,119.07       $1,216.2381   $1,216.24   $1,216.25   $1,216.20