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 $208.31   10.320%   $229.8076   $229.81   $229.80   $229.80  
  Purchase #2 $231.25   10.103%   $254.6132   $254.61   $254.60   $254.60  
  Purchase #3 $124.59   4.725%   $130.4769   $130.48   $130.50   $130.50  
  Purchase #4 $39.67   11.358%   $44.1757   $44.18   $44.20   $44.20  
  Purchase #5 $205.76   3.473%   $212.906   $212.91   $212.90   $212.90  
  Purchase #6 $21.47   4.389%   $22.4123   $22.41   $22.40   $22.40  
  Purchase #7 $246.96   10.309%   $272.4191   $272.42   $272.40   $272.40  
  7 purchase totals = $1,078.01       $1,166.8108   $1,166.82   $1,166.80   $1,166.80