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 $203.59   11.471%   $226.9438   $226.94   $226.95   $226.90  
  Purchase #2 $11.58   5.814%   $12.2533   $12.25   $12.25   $12.30  
  Purchase #3 $17.28   4.188%   $18.0037   $18.00   $18.00   $18.00  
  Purchase #4 $42.92   5.748%   $45.387   $45.39   $45.40   $45.40  
  Purchase #5 $164.74   6.456%   $175.3756   $175.38   $175.40   $175.40  
  Purchase #6 $185.87   3.329%   $192.0576   $192.06   $192.05   $192.10  
  Purchase #7 $192.71   6.498%   $205.2323   $205.23   $205.25   $205.20  
  7 purchase totals = $818.69       $875.2533   $875.25   $875.30   $875.30