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 $177.35   12.105%   $198.8182   $198.82   $198.80   $198.80  
  Purchase #2 $176.91   9.343%   $193.4387   $193.44   $193.45   $193.40  
  Purchase #3 $92.40   5.813%   $97.7712   $97.77   $97.75   $97.80  
  Purchase #4 $208.45   5.134%   $219.1518   $219.15   $219.15   $219.20  
  Purchase #5 $66.67   13.262%   $75.5118   $75.51   $75.50   $75.50  
  Purchase #6 $179.81   13.605%   $204.2732   $204.27   $204.25   $204.30  
  Purchase #7 $109.67   10.755%   $121.465   $121.47   $121.45   $121.50  
  7 purchase totals = $1,011.26       $1,110.4299   $1,110.43   $1,110.35   $1,110.50