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 $227.47   9.757%   $249.6642   $249.66   $249.65   $249.70  
  Purchase #2 $170.68   11.690%   $190.6325   $190.63   $190.65   $190.60  
  Purchase #3 $18.70   4.382%   $19.5194   $19.52   $19.50   $19.50  
  Purchase #4 $30.53   9.782%   $33.5164   $33.52   $33.50   $33.50  
  Purchase #5 $204.78   4.269%   $213.5221   $213.52   $213.50   $213.50  
  Purchase #6 $237.49   10.508%   $262.4454   $262.45   $262.45   $262.40  
  Purchase #7 $221.49   8.814%   $241.0121   $241.01   $241.00   $241.00  
  7 purchase totals = $1,111.14       $1,210.3121   $1,210.31   $1,210.25   $1,210.20