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 $144.67   6.635%   $154.2689   $154.27   $154.25   $154.30  
  Purchase #2 $33.97   6.599%   $36.2117   $36.21   $36.20   $36.20  
  Purchase #3 $109.96   13.333%   $124.621   $124.62   $124.60   $124.60  
  Purchase #4 $230.77   7.223%   $247.4385   $247.44   $247.45   $247.40  
  Purchase #5 $137.61   5.473%   $145.1414   $145.14   $145.15   $145.10  
  Purchase #6 $169.40   11.554%   $188.9725   $188.97   $188.95   $189.00  
  Purchase #7 $130.91   7.536%   $140.7754   $140.78   $140.80   $140.80  
  7 purchase totals = $957.29       $1,037.4294   $1,037.43   $1,037.40   $1,037.40