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 $69.94   4.757%   $73.267   $73.27   $73.25   $73.30  
  Purchase #2 $12.43   8.518%   $13.4888   $13.49   $13.50   $13.50  
  Purchase #3 $182.97   13.153%   $207.036   $207.04   $207.05   $207.00  
  Purchase #4 $127.38   4.313%   $132.8739   $132.87   $132.85   $132.90  
  Purchase #5 $158.70   3.268%   $163.8863   $163.89   $163.90   $163.90  
  Purchase #6 $244.77   9.414%   $267.8126   $267.81   $267.80   $267.80  
  Purchase #7 $188.27   12.615%   $212.0203   $212.02   $212.00   $212.00  
  7 purchase totals = $984.46       $1,070.3849   $1,070.39   $1,070.35   $1,070.40