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 $145.51   5.660%   $153.7459   $153.75   $153.75   $153.70  
  Purchase #2 $205.25   6.216%   $218.0083   $218.01   $218.00   $218.00  
  Purchase #3 $188.48   6.493%   $200.718   $200.72   $200.70   $200.70  
  Purchase #4 $152.42   4.211%   $158.8384   $158.84   $158.85   $158.80  
  Purchase #5 $97.57   3.821%   $101.2981   $101.30   $101.30   $101.30  
  Purchase #6 $241.56   5.835%   $255.655   $255.66   $255.65   $255.70  
  Purchase #7 $195.74   11.808%   $218.853   $218.85   $218.85   $218.90  
  7 purchase totals = $1,226.53       $1,307.1167   $1,307.13   $1,307.10   $1,307.10