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 $204.54   11.128%   $227.3012   $227.30   $227.30   $227.30  
  Purchase #2 $21.28   10.128%   $23.4352   $23.44   $23.45   $23.40  
  Purchase #3 $68.53   9.702%   $75.1788   $75.18   $75.20   $75.20  
  Purchase #4 $170.47   5.607%   $180.0283   $180.03   $180.05   $180.00  
  Purchase #5 $184.74   4.743%   $193.5022   $193.50   $193.50   $193.50  
  Purchase #6 $151.88   12.426%   $170.7526   $170.75   $170.75   $170.80  
  Purchase #7 $13.64   6.869%   $14.5769   $14.58   $14.60   $14.60  
  7 purchase totals = $815.08       $884.7752   $884.78   $884.85   $884.80