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 $108.70   13.671%   $123.5604   $123.56   $123.55   $123.60  
  Purchase #2 $203.48   11.413%   $226.7032   $226.70   $226.70   $226.70  
  Purchase #3 $23.31   12.862%   $26.3081   $26.31   $26.30   $26.30  
  Purchase #4 $129.62   3.768%   $134.5041   $134.50   $134.50   $134.50  
  Purchase #5 $50.63   10.223%   $55.8059   $55.81   $55.80   $55.80  
  Purchase #6 $219.78   9.631%   $240.947   $240.95   $240.95   $240.90  
  Purchase #7 $56.71   4.757%   $59.4077   $59.41   $59.40   $59.40  
  7 purchase totals = $792.23       $867.2364   $867.24   $867.20   $867.20