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 $32.29   7.364%   $34.6678   $34.67   $34.65   $34.70  
  Purchase #2 $141.87   5.238%   $149.3012   $149.30   $149.30   $149.30  
  Purchase #3 $198.94   9.540%   $217.9189   $217.92   $217.90   $217.90  
  Purchase #4 $111.77   5.712%   $118.1543   $118.15   $118.15   $118.20  
  Purchase #5 $67.26   8.787%   $73.1701   $73.17   $73.15   $73.20  
  Purchase #6 $104.52   5.833%   $110.6167   $110.62   $110.60   $110.60  
  Purchase #7 $177.64   7.197%   $190.4248   $190.42   $190.40   $190.40  
  7 purchase totals = $834.29       $894.2538   $894.25   $894.15   $894.30