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 $207.36   5.272%   $218.292   $218.29   $218.30   $218.30  
  Purchase #2 $70.35   5.700%   $74.36   $74.36   $74.35   $74.40  
  Purchase #3 $58.90   12.513%   $66.2702   $66.27   $66.25   $66.30  
  Purchase #4 $169.32   4.324%   $176.6414   $176.64   $176.65   $176.60  
  Purchase #5 $183.97   5.366%   $193.8418   $193.84   $193.85   $193.80  
  Purchase #6 $16.74   3.232%   $17.281   $17.28   $17.30   $17.30  
  Purchase #7 $129.69   5.411%   $136.7075   $136.71   $136.70   $136.70  
  7 purchase totals = $836.33       $883.3939   $883.39   $883.40   $883.40