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 $63.81   13.696%   $72.5494   $72.55   $72.55   $72.50  
  Purchase #2 $135.94   13.176%   $153.8515   $153.85   $153.85   $153.90  
  Purchase #3 $209.86   12.821%   $236.7662   $236.77   $236.75   $236.80  
  Purchase #4 $246.58   13.732%   $280.4404   $280.44   $280.45   $280.40  
  Purchase #5 $230.65   10.212%   $254.204   $254.20   $254.20   $254.20  
  Purchase #6 $209.88   9.200%   $229.189   $229.19   $229.20   $229.20  
  Purchase #7 $237.52   8.248%   $257.1106   $257.11   $257.10   $257.10  
  7 purchase totals = $1,334.24       $1,484.1111   $1,484.11   $1,484.10   $1,484.10