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 $59.35   10.209%   $65.409   $65.41   $65.40   $65.40  
  Purchase #2 $234.55   12.530%   $263.9391   $263.94   $263.95   $263.90  
  Purchase #3 $55.93   10.436%   $61.7669   $61.77   $61.75   $61.80  
  Purchase #4 $111.47   7.183%   $119.4769   $119.48   $119.50   $119.50  
  Purchase #5 $249.69   6.833%   $266.7513   $266.75   $266.75   $266.80  
  Purchase #6 $119.33   8.544%   $129.5256   $129.53   $129.55   $129.50  
  Purchase #7 $103.93   12.407%   $116.8246   $116.82   $116.80   $116.80  
  7 purchase totals = $934.25       $1,023.6934   $1,023.70   $1,023.70   $1,023.70