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 $106.29   12.434%   $119.5061   $119.51   $119.50   $119.50  
  Purchase #2 $138.27   4.352%   $144.2875   $144.29   $144.30   $144.30  
  Purchase #3 $163.60   5.567%   $172.7076   $172.71   $172.70   $172.70  
  Purchase #4 $159.35   5.120%   $167.5087   $167.51   $167.50   $167.50  
  Purchase #5 $124.32   9.420%   $136.0309   $136.03   $136.05   $136.00  
  Purchase #6 $215.29   9.299%   $235.3098   $235.31   $235.30   $235.30  
  Purchase #7 $249.57   9.744%   $273.8881   $273.89   $273.90   $273.90  
  7 purchase totals = $1,156.69       $1,249.2387   $1,249.25   $1,249.25   $1,249.20