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 $216.80   11.187%   $241.0534   $241.05   $241.05   $241.10  
  Purchase #2 $122.88   5.401%   $129.5167   $129.52   $129.50   $129.50  
  Purchase #3 $52.26   9.575%   $57.2639   $57.26   $57.25   $57.30  
  Purchase #4 $126.39   9.133%   $137.9332   $137.93   $137.95   $137.90  
  Purchase #5 $227.57   5.235%   $239.4833   $239.48   $239.50   $239.50  
  Purchase #6 $79.25   9.211%   $86.5497   $86.55   $86.55   $86.50  
  Purchase #7 $110.86   9.725%   $121.6411   $121.64   $121.65   $121.60  
  7 purchase totals = $936.01       $1,013.4413   $1,013.43   $1,013.45   $1,013.40