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 $34.83   7.190%   $37.3343   $37.33   $37.35   $37.30  
  Purchase #2 $237.82   3.742%   $246.7192   $246.72   $246.70   $246.70  
  Purchase #3 $109.86   7.762%   $118.3873   $118.39   $118.40   $118.40  
  Purchase #4 $208.86   7.449%   $224.418   $224.42   $224.40   $224.40  
  Purchase #5 $8.82   3.806%   $9.1557   $9.16   $9.15   $9.20  
  Purchase #6 $186.59   9.686%   $204.6631   $204.66   $204.65   $204.70  
  Purchase #7 $47.52   12.636%   $53.5246   $53.52   $53.50   $53.50  
  7 purchase totals = $834.30       $894.2022   $894.20   $894.15   $894.20