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 $13.53   6.276%   $14.3791   $14.38   $14.40   $14.40  
  Purchase #2 $208.56   12.302%   $234.2171   $234.22   $234.20   $234.20  
  Purchase #3 $236.86   10.391%   $261.4721   $261.47   $261.45   $261.50  
  Purchase #4 $223.95   5.494%   $236.2538   $236.25   $236.25   $236.30  
  Purchase #5 $120.29   12.514%   $135.3431   $135.34   $135.35   $135.30  
  Purchase #6 $118.88   12.649%   $133.9171   $133.92   $133.90   $133.90  
  Purchase #7 $184.52   9.282%   $201.6471   $201.65   $201.65   $201.60  
  7 purchase totals = $1,106.59       $1,217.2294   $1,217.23   $1,217.20   $1,217.20