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 $46.65   7.212%   $50.0144   $50.01   $50.00   $50.00  
  Purchase #2 $63.67   12.706%   $71.7599   $71.76   $71.75   $71.80  
  Purchase #3 $101.74   11.649%   $113.5917   $113.59   $113.60   $113.60  
  Purchase #4 $216.46   11.574%   $241.5131   $241.51   $241.50   $241.50  
  Purchase #5 $72.89   9.712%   $79.9691   $79.97   $79.95   $80.00  
  Purchase #6 $92.86   5.644%   $98.101   $98.10   $98.10   $98.10  
  Purchase #7 $190.52   6.389%   $202.6923   $202.69   $202.70   $202.70  
  7 purchase totals = $784.79       $857.6415   $857.63   $857.60   $857.70