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 $87.44   12.300%   $98.1951   $98.20   $98.20   $98.20  
  Purchase #2 $194.36   3.390%   $200.9488   $200.95   $200.95   $200.90  
  Purchase #3 $8.71   5.533%   $9.1919   $9.19   $9.20   $9.20  
  Purchase #4 $184.40   11.365%   $205.3571   $205.36   $205.35   $205.40  
  Purchase #5 $171.51   10.588%   $189.6695   $189.67   $189.65   $189.70  
  Purchase #6 $186.50   13.811%   $212.2575   $212.26   $212.25   $212.30  
  Purchase #7 $143.38   11.313%   $159.6006   $159.60   $159.60   $159.60  
  7 purchase totals = $976.30       $1,075.2205   $1,075.23   $1,075.20   $1,075.30