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 $191.46   6.189%   $203.3095   $203.31   $203.30   $203.30  
  Purchase #2 $214.43   3.485%   $221.9029   $221.90   $221.90   $221.90  
  Purchase #3 $49.41   4.857%   $51.8098   $51.81   $51.80   $51.80  
  Purchase #4 $178.84   9.732%   $196.2447   $196.24   $196.25   $196.20  
  Purchase #5 $10.92   4.398%   $11.4003   $11.40   $11.40   $11.40  
  Purchase #6 $202.47   6.160%   $214.9422   $214.94   $214.95   $214.90  
  Purchase #7 $126.96   11.803%   $141.9451   $141.95   $141.95   $141.90  
  7 purchase totals = $974.49       $1,041.5545   $1,041.55   $1,041.55   $1,041.40