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 $67.32   12.479%   $75.7209   $75.72   $75.70   $75.70  
  Purchase #2 $170.97   7.299%   $183.4491   $183.45   $183.45   $183.40  
  Purchase #3 $150.49   8.370%   $163.086   $163.09   $163.10   $163.10  
  Purchase #4 $139.37   8.367%   $151.0311   $151.03   $151.05   $151.00  
  Purchase #5 $53.86   5.865%   $57.0189   $57.02   $57.00   $57.00  
  Purchase #6 $119.76   12.834%   $135.13   $135.13   $135.15   $135.10  
  Purchase #7 $174.82   8.849%   $190.2898   $190.29   $190.30   $190.30  
  7 purchase totals = $876.59       $955.7258   $955.73   $955.75   $955.60