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 $91.36   7.547%   $98.2549   $98.25   $98.25   $98.30  
  Purchase #2 $179.78   4.314%   $187.5357   $187.54   $187.55   $187.50  
  Purchase #3 $139.30   10.378%   $153.7566   $153.76   $153.75   $153.80  
  Purchase #4 $189.99   7.872%   $204.946   $204.95   $204.95   $204.90  
  Purchase #5 $136.37   5.129%   $143.3644   $143.36   $143.35   $143.40  
  Purchase #6 $208.78   5.605%   $220.4821   $220.48   $220.50   $220.50  
  Purchase #7 $98.51   5.869%   $104.2916   $104.29   $104.30   $104.30  
  7 purchase totals = $1,044.09       $1,112.6313   $1,112.63   $1,112.65   $1,112.70