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 $240.95   11.686%   $269.1074   $269.11   $269.10   $269.10  
  Purchase #2 $222.84   9.463%   $243.9273   $243.93   $243.95   $243.90  
  Purchase #3 $39.93   8.640%   $43.38   $43.38   $43.40   $43.40  
  Purchase #4 $127.29   13.773%   $144.8217   $144.82   $144.80   $144.80  
  Purchase #5 $27.87   4.854%   $29.2228   $29.22   $29.20   $29.20  
  Purchase #6 $42.83   13.807%   $48.7435   $48.74   $48.75   $48.70  
  Purchase #7 $94.41   7.638%   $101.621   $101.62   $101.60   $101.60  
  7 purchase totals = $796.12       $880.8237   $880.82   $880.80   $880.70