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 $54.89   13.565%   $62.3358   $62.34   $62.35   $62.30  
  Purchase #2 $132.56   3.509%   $137.2115   $137.21   $137.20   $137.20  
  Purchase #3 $189.65   6.357%   $201.7061   $201.71   $201.70   $201.70  
  Purchase #4 $125.64   5.712%   $132.8166   $132.82   $132.80   $132.80  
  Purchase #5 $233.90   5.845%   $247.5715   $247.57   $247.55   $247.60  
  Purchase #6 $57.51   8.769%   $62.5531   $62.55   $62.55   $62.60  
  Purchase #7 $39.39   8.768%   $42.8437   $42.84   $42.85   $42.80  
  7 purchase totals = $833.54       $887.0383   $887.04   $887.00   $887.00