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 $218.74   8.143%   $236.552   $236.55   $236.55   $236.60  
  Purchase #2 $191.38   5.755%   $202.3939   $202.39   $202.40   $202.40  
  Purchase #3 $131.35   6.435%   $139.8024   $139.80   $139.80   $139.80  
  Purchase #4 $46.90   4.275%   $48.905   $48.91   $48.90   $48.90  
  Purchase #5 $93.49   4.254%   $97.4671   $97.47   $97.45   $97.50  
  Purchase #6 $119.72   6.779%   $127.8358   $127.84   $127.85   $127.80  
  Purchase #7 $86.82   11.642%   $96.9276   $96.93   $96.95   $96.90  
  7 purchase totals = $888.40       $949.8838   $949.89   $949.90   $949.90