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 $70.67   4.114%   $73.5774   $73.58   $73.60   $73.60  
  Purchase #2 $161.36   9.263%   $176.3068   $176.31   $176.30   $176.30  
  Purchase #3 $55.36   7.645%   $59.5923   $59.59   $59.60   $59.60  
  Purchase #4 $207.42   10.751%   $229.7197   $229.72   $229.70   $229.70  
  Purchase #5 $17.50   7.249%   $18.7686   $18.77   $18.75   $18.80  
  Purchase #6 $112.60   11.851%   $125.9442   $125.94   $125.95   $125.90  
  Purchase #7 $184.56   10.532%   $203.9979   $204.00   $204.00   $204.00  
  7 purchase totals = $809.47       $887.9069   $887.91   $887.90   $887.90