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 $182.48   10.579%   $201.7846   $201.78   $201.80   $201.80  
  Purchase #2 $118.28   6.249%   $125.6713   $125.67   $125.65   $125.70  
  Purchase #3 $37.53   6.771%   $40.0712   $40.07   $40.05   $40.10  
  Purchase #4 $232.51   8.289%   $251.7828   $251.78   $251.80   $251.80  
  Purchase #5 $33.86   9.751%   $37.1617   $37.16   $37.15   $37.20  
  Purchase #6 $92.92   5.776%   $98.2871   $98.29   $98.30   $98.30  
  Purchase #7 $165.81   7.606%   $178.4215   $178.42   $178.40   $178.40  
  7 purchase totals = $863.39       $933.1802   $933.17   $933.15   $933.30