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 $235.27   7.120%   $252.0212   $252.02   $252.00   $252.00  
  Purchase #2 $96.28   7.840%   $103.8284   $103.83   $103.85   $103.80  
  Purchase #3 $211.34   9.255%   $230.8995   $230.90   $230.90   $230.90  
  Purchase #4 $92.64   5.123%   $97.3859   $97.39   $97.40   $97.40  
  Purchase #5 $150.83   4.758%   $158.0065   $158.01   $158.00   $158.00  
  Purchase #6 $232.55   12.109%   $260.7095   $260.71   $260.70   $260.70  
  Purchase #7 $169.62   8.119%   $183.3914   $183.39   $183.40   $183.40  
  7 purchase totals = $1,188.53       $1,286.2424   $1,286.25   $1,286.25   $1,286.20