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 $72.67   4.492%   $75.9343   $75.93   $75.95   $75.90  
  Purchase #2 $88.83   13.665%   $100.9686   $100.97   $100.95   $101.00  
  Purchase #3 $249.43   9.474%   $273.061   $273.06   $273.05   $273.10  
  Purchase #4 $249.62   6.737%   $266.4369   $266.44   $266.45   $266.40  
  Purchase #5 $224.85   9.171%   $245.471   $245.47   $245.45   $245.50  
  Purchase #6 $25.99   5.550%   $27.4324   $27.43   $27.45   $27.40  
  Purchase #7 $237.51   11.329%   $264.4175   $264.42   $264.40   $264.40  
  7 purchase totals = $1,148.90       $1,253.7217   $1,253.72   $1,253.70   $1,253.70