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 $245.73   9.546%   $269.1874   $269.19   $269.20   $269.20  
  Purchase #2 $96.48   11.600%   $107.6717   $107.67   $107.65   $107.70  
  Purchase #3 $145.75   8.743%   $158.4929   $158.49   $158.50   $158.50  
  Purchase #4 $25.34   10.221%   $27.93   $27.93   $27.95   $27.90  
  Purchase #5 $204.84   12.190%   $229.81   $229.81   $229.80   $229.80  
  Purchase #6 $208.78   10.493%   $230.6873   $230.69   $230.70   $230.70  
  Purchase #7 $248.99   11.629%   $277.945   $277.95   $277.95   $277.90  
  7 purchase totals = $1,175.91       $1,301.7243   $1,301.73   $1,301.75   $1,301.70