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 $83.52   11.760%   $93.342   $93.34   $93.35   $93.30  
  Purchase #2 $192.51   6.105%   $204.2627   $204.26   $204.25   $204.30  
  Purchase #3 $129.92   10.485%   $143.5421   $143.54   $143.55   $143.50  
  Purchase #4 $201.77   7.739%   $217.385   $217.39   $217.40   $217.40  
  Purchase #5 $169.37   13.575%   $192.362   $192.36   $192.35   $192.40  
  Purchase #6 $65.96   3.524%   $68.2844   $68.28   $68.30   $68.30  
  Purchase #7 $225.84   5.267%   $237.735   $237.74   $237.75   $237.70  
  7 purchase totals = $1,068.89       $1,156.9132   $1,156.91   $1,156.95   $1,156.90