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 $161.33   7.702%   $173.7556   $173.76   $173.75   $173.80  
  Purchase #2 $204.87   4.208%   $213.4909   $213.49   $213.50   $213.50  
  Purchase #3 $21.54   7.158%   $23.0818   $23.08   $23.10   $23.10  
  Purchase #4 $195.50   9.785%   $214.6297   $214.63   $214.65   $214.60  
  Purchase #5 $39.80   9.248%   $43.4807   $43.48   $43.50   $43.50  
  Purchase #6 $171.40   13.229%   $194.0745   $194.07   $194.05   $194.10  
  Purchase #7 $174.83   11.198%   $194.4075   $194.41   $194.40   $194.40  
  7 purchase totals = $969.27       $1,056.9207   $1,056.92   $1,056.95   $1,057.00