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 $115.66   4.300%   $120.6334   $120.63   $120.65   $120.60  
  Purchase #2 $232.81   5.711%   $246.1058   $246.11   $246.10   $246.10  
  Purchase #3 $217.90   3.865%   $226.3218   $226.32   $226.30   $226.30  
  Purchase #4 $36.43   8.462%   $39.5127   $39.51   $39.50   $39.50  
  Purchase #5 $159.76   9.452%   $174.8605   $174.86   $174.85   $174.90  
  Purchase #6 $193.97   5.701%   $205.0282   $205.03   $205.05   $205.00  
  Purchase #7 $220.60   7.648%   $237.4715   $237.47   $237.45   $237.50  
  7 purchase totals = $1,177.13       $1,249.9339   $1,249.93   $1,249.90   $1,249.90