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 $180.93   10.132%   $199.2618   $199.26   $199.25   $199.30  
  Purchase #2 $109.33   11.251%   $121.6307   $121.63   $121.65   $121.60  
  Purchase #3 $63.79   7.488%   $68.5666   $68.57   $68.55   $68.60  
  Purchase #4 $87.65   11.476%   $97.7087   $97.71   $97.70   $97.70  
  Purchase #5 $189.83   7.108%   $203.3231   $203.32   $203.30   $203.30  
  Purchase #6 $250.82   9.503%   $274.6554   $274.66   $274.65   $274.70  
  Purchase #7 $191.97   13.580%   $218.0395   $218.04   $218.05   $218.00  
  7 purchase totals = $1,074.32       $1,183.1858   $1,183.19   $1,183.15   $1,183.20