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 $248.52   11.165%   $276.2673   $276.27   $276.25   $276.30  
  Purchase #2 $55.63   12.836%   $62.7707   $62.77   $62.75   $62.80  
  Purchase #3 $244.83   12.802%   $276.1731   $276.17   $276.15   $276.20  
  Purchase #4 $190.44   11.213%   $211.794   $211.79   $211.80   $211.80  
  Purchase #5 $193.32   8.396%   $209.5511   $209.55   $209.55   $209.60  
  Purchase #6 $31.57   11.588%   $35.2283   $35.23   $35.25   $35.20  
  Purchase #7 $143.33   5.502%   $151.216   $151.22   $151.20   $151.20  
  7 purchase totals = $1,107.64       $1,223.0005   $1,223.00   $1,222.95   $1,223.10