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 $86.81   9.497%   $95.0543   $95.05   $95.05   $95.10  
  Purchase #2 $210.50   6.111%   $223.3637   $223.36   $223.35   $223.40  
  Purchase #3 $67.29   11.657%   $75.134   $75.13   $75.15   $75.10  
  Purchase #4 $18.74   8.183%   $20.2735   $20.27   $20.25   $20.30  
  Purchase #5 $81.74   3.576%   $84.663   $84.66   $84.65   $84.70  
  Purchase #6 $214.82   8.632%   $233.3633   $233.36   $233.35   $233.40  
  Purchase #7 $45.36   5.210%   $47.7233   $47.72   $47.70   $47.70  
  7 purchase totals = $725.26       $779.5751   $779.55   $779.50   $779.70