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 $248.33   5.420%   $261.7895   $261.79   $261.80   $261.80  
  Purchase #2 $54.52   3.858%   $56.6234   $56.62   $56.60   $56.60  
  Purchase #3 $207.46   12.485%   $233.3614   $233.36   $233.35   $233.40  
  Purchase #4 $101.55   10.268%   $111.9772   $111.98   $112.00   $112.00  
  Purchase #5 $161.94   4.602%   $169.3925   $169.39   $169.40   $169.40  
  Purchase #6 $179.49   12.540%   $201.998   $202.00   $202.00   $202.00  
  Purchase #7 $154.90   5.643%   $163.641   $163.64   $163.65   $163.60  
  7 purchase totals = $1,108.19       $1,198.7830   $1,198.78   $1,198.80   $1,198.80