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 $48.68   12.653%   $54.8395   $54.84   $54.85   $54.80  
  Purchase #2 $245.41   9.266%   $268.1497   $268.15   $268.15   $268.10  
  Purchase #3 $217.34   8.779%   $236.4203   $236.42   $236.40   $236.40  
  Purchase #4 $18.78   7.344%   $20.1592   $20.16   $20.15   $20.20  
  Purchase #5 $77.33   7.229%   $82.9202   $82.92   $82.90   $82.90  
  Purchase #6 $57.86   3.673%   $59.9852   $59.99   $60.00   $60.00  
  Purchase #7 $200.29   12.613%   $225.5526   $225.55   $225.55   $225.60  
  7 purchase totals = $865.69       $948.0267   $948.03   $948.00   $948.00