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 $58.80   11.194%   $65.3821   $65.38   $65.40   $65.40  
  Purchase #2 $72.72   6.849%   $77.7006   $77.70   $77.70   $77.70  
  Purchase #3 $241.66   5.519%   $254.9972   $255.00   $255.00   $255.00  
  Purchase #4 $226.29   8.787%   $246.1741   $246.17   $246.15   $246.20  
  Purchase #5 $15.90   3.727%   $16.4926   $16.49   $16.50   $16.50  
  Purchase #6 $159.44   12.341%   $179.1165   $179.12   $179.10   $179.10  
  Purchase #7 $218.26   4.213%   $227.4553   $227.46   $227.45   $227.50  
  7 purchase totals = $993.07       $1,067.3184   $1,067.32   $1,067.30   $1,067.40