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 $32.83   5.497%   $34.6347   $34.63   $34.65   $34.60  
  Purchase #2 $113.59   3.521%   $117.5895   $117.59   $117.60   $117.60  
  Purchase #3 $218.34   4.412%   $227.9732   $227.97   $227.95   $228.00  
  Purchase #4 $194.69   7.790%   $209.8564   $209.86   $209.85   $209.90  
  Purchase #5 $6.70   3.523%   $6.936   $6.94   $6.95   $6.90  
  Purchase #6 $61.53   3.704%   $63.8091   $63.81   $63.80   $63.80  
  Purchase #7 $87.32   7.592%   $93.9493   $93.95   $93.95   $93.90  
  7 purchase totals = $715.00       $754.7482   $754.75   $754.75   $754.70