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 $67.34   3.722%   $69.8464   $69.85   $69.85   $69.80  
  Purchase #2 $209.98   8.550%   $227.9333   $227.93   $227.95   $227.90  
  Purchase #3 $30.88   9.245%   $33.7349   $33.73   $33.75   $33.70  
  Purchase #4 $76.27   3.833%   $79.1934   $79.19   $79.20   $79.20  
  Purchase #5 $208.93   8.297%   $226.2649   $226.26   $226.25   $226.30  
  Purchase #6 $71.92   4.842%   $75.4024   $75.40   $75.40   $75.40  
  Purchase #7 $202.83   5.690%   $214.371   $214.37   $214.35   $214.40  
  7 purchase totals = $868.15       $926.7463   $926.73   $926.75   $926.70