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 $223.87   10.342%   $247.0226   $247.02   $247.00   $247.00  
  Purchase #2 $204.27   8.365%   $221.3572   $221.36   $221.35   $221.40  
  Purchase #3 $157.37   7.607%   $169.3411   $169.34   $169.35   $169.30  
  Purchase #4 $244.37   5.862%   $258.695   $258.70   $258.70   $258.70  
  Purchase #5 $76.74   13.332%   $86.971   $86.97   $86.95   $87.00  
  Purchase #6 $176.49   8.159%   $190.8898   $190.89   $190.90   $190.90  
  Purchase #7 $132.92   12.140%   $149.0565   $149.06   $149.05   $149.10  
  7 purchase totals = $1,216.03       $1,323.3332   $1,323.34   $1,323.30   $1,323.40