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 $108.89   9.686%   $119.4371   $119.44   $119.45   $119.40  
  Purchase #2 $97.44   9.442%   $106.6403   $106.64   $106.65   $106.60  
  Purchase #3 $43.35   12.807%   $48.9018   $48.90   $48.90   $48.90  
  Purchase #4 $95.46   12.450%   $107.3448   $107.34   $107.35   $107.30  
  Purchase #5 $185.40   10.780%   $205.3861   $205.39   $205.40   $205.40  
  Purchase #6 $213.25   11.538%   $237.8548   $237.85   $237.85   $237.90  
  Purchase #7 $95.74   3.788%   $99.3666   $99.37   $99.35   $99.40  
  7 purchase totals = $839.53       $924.9315   $924.93   $924.95   $924.90