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 $65.92   8.159%   $71.2984   $71.30   $71.30   $71.30  
  Purchase #2 $199.53   8.167%   $215.8256   $215.83   $215.85   $215.80  
  Purchase #3 $10.49   13.778%   $11.9353   $11.94   $11.95   $11.90  
  Purchase #4 $185.41   12.603%   $208.7772   $208.78   $208.80   $208.80  
  Purchase #5 $7.92   12.692%   $8.9252   $8.93   $8.95   $8.90  
  Purchase #6 $177.48   12.327%   $199.358   $199.36   $199.35   $199.40  
  Purchase #7 $164.72   7.675%   $177.3623   $177.36   $177.35   $177.40  
  7 purchase totals = $811.47       $893.4820   $893.50   $893.55   $893.50