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 $185.70   11.753%   $207.5253   $207.53   $207.55   $207.50  
  Purchase #2 $167.65   9.546%   $183.6539   $183.65   $183.65   $183.70  
  Purchase #3 $153.69   13.391%   $174.2706   $174.27   $174.25   $174.30  
  Purchase #4 $52.29   4.564%   $54.6765   $54.68   $54.70   $54.70  
  Purchase #5 $117.42   8.261%   $127.1201   $127.12   $127.10   $127.10  
  Purchase #6 $97.65   3.303%   $100.8754   $100.88   $100.90   $100.90  
  Purchase #7 $21.64   4.261%   $22.5621   $22.56   $22.55   $22.60  
  7 purchase totals = $796.04       $870.6839   $870.69   $870.70   $870.80