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 $51.69   4.672%   $54.105   $54.11   $54.10   $54.10  
  Purchase #2 $189.28   10.588%   $209.321   $209.32   $209.30   $209.30  
  Purchase #3 $222.33   8.622%   $241.4993   $241.50   $241.50   $241.50  
  Purchase #4 $58.74   5.124%   $61.7498   $61.75   $61.75   $61.70  
  Purchase #5 $250.63   6.766%   $267.5876   $267.59   $267.60   $267.60  
  Purchase #6 $9.26   7.469%   $9.9516   $9.95   $9.95   $10.00  
  Purchase #7 $188.68   8.751%   $205.1914   $205.19   $205.20   $205.20  
  7 purchase totals = $970.61       $1,049.4057   $1,049.41   $1,049.40   $1,049.40