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 $55.97   10.102%   $61.6241   $61.62   $61.60   $61.60  
  Purchase #2 $43.74   9.614%   $47.9452   $47.95   $47.95   $47.90  
  Purchase #3 $98.84   5.813%   $104.5856   $104.59   $104.60   $104.60  
  Purchase #4 $29.98   9.181%   $32.7325   $32.73   $32.75   $32.70  
  Purchase #5 $184.83   11.245%   $205.6141   $205.61   $205.60   $205.60  
  Purchase #6 $51.80   8.834%   $56.376   $56.38   $56.40   $56.40  
  Purchase #7 $101.54   8.765%   $110.44   $110.44   $110.45   $110.40  
  7 purchase totals = $566.70       $619.3175   $619.32   $619.35   $619.20