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 $62.96   3.337%   $65.061   $65.06   $65.05   $65.10  
  Purchase #2 $23.31   4.374%   $24.3296   $24.33   $24.35   $24.30  
  Purchase #3 $38.31   5.625%   $40.4649   $40.46   $40.45   $40.50  
  Purchase #4 $47.79   4.617%   $49.9965   $50.00   $50.00   $50.00  
  Purchase #5 $200.43   4.425%   $209.299   $209.30   $209.30   $209.30  
  Purchase #6 $248.80   10.469%   $274.8469   $274.85   $274.85   $274.80  
  Purchase #7 $51.75   3.749%   $53.6901   $53.69   $53.70   $53.70  
  7 purchase totals = $673.35       $717.6880   $717.69   $717.70   $717.70