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 $184.58   11.557%   $205.9119   $205.91   $205.90   $205.90  
  Purchase #2 $167.97   3.749%   $174.2672   $174.27   $174.25   $174.30  
  Purchase #3 $32.54   12.800%   $36.7051   $36.71   $36.70   $36.70  
  Purchase #4 $191.63   12.452%   $215.4918   $215.49   $215.50   $215.50  
  Purchase #5 $34.71   4.768%   $36.365   $36.37   $36.35   $36.40  
  Purchase #6 $25.30   3.398%   $26.1597   $26.16   $26.15   $26.20  
  Purchase #7 $205.70   12.458%   $231.3261   $231.33   $231.35   $231.30  
  7 purchase totals = $842.43       $926.2268   $926.24   $926.20   $926.30