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 $239.65   10.128%   $263.9218   $263.92   $263.90   $263.90  
  Purchase #2 $105.26   6.677%   $112.2882   $112.29   $112.30   $112.30  
  Purchase #3 $195.38   10.606%   $216.102   $216.10   $216.10   $216.10  
  Purchase #4 $153.55   5.281%   $161.659   $161.66   $161.65   $161.70  
  Purchase #5 $36.77   7.472%   $39.5175   $39.52   $39.50   $39.50  
  Purchase #6 $222.42   5.342%   $234.3017   $234.30   $234.30   $234.30  
  Purchase #7 $117.91   4.570%   $123.2985   $123.30   $123.30   $123.30  
  7 purchase totals = $1,070.94       $1,151.0887   $1,151.09   $1,151.05   $1,151.10