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 $230.90   5.308%   $243.1562   $243.16   $243.15   $243.20  
  Purchase #2 $246.77   7.462%   $265.184   $265.18   $265.20   $265.20  
  Purchase #3 $177.73   6.738%   $189.7054   $189.71   $189.70   $189.70  
  Purchase #4 $19.88   5.113%   $20.8965   $20.90   $20.90   $20.90  
  Purchase #5 $170.50   9.716%   $187.0658   $187.07   $187.05   $187.10  
  Purchase #6 $241.90   10.289%   $266.7891   $266.79   $266.80   $266.80  
  Purchase #7 $49.30   11.595%   $55.0163   $55.02   $55.00   $55.00  
  7 purchase totals = $1,136.98       $1,227.8133   $1,227.83   $1,227.80   $1,227.90