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 $60.64   4.800%   $63.5507   $63.55   $63.55   $63.60  
  Purchase #2 $194.64   5.491%   $205.3277   $205.33   $205.35   $205.30  
  Purchase #3 $192.54   6.229%   $204.5333   $204.53   $204.55   $204.50  
  Purchase #4 $52.84   3.265%   $54.5652   $54.57   $54.55   $54.60  
  Purchase #5 $71.49   4.774%   $74.9029   $74.90   $74.90   $74.90  
  Purchase #6 $54.88   12.157%   $61.5518   $61.55   $61.55   $61.60  
  Purchase #7 $13.90   9.118%   $15.1674   $15.17   $15.15   $15.20  
  7 purchase totals = $640.93       $679.5990   $679.60   $679.60   $679.70