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 $60.69   11.838%   $67.8745   $67.87   $67.85   $67.90  
  Purchase #2 $192.51   7.260%   $206.4862   $206.49   $206.50   $206.50  
  Purchase #3 $223.88   5.577%   $236.3658   $236.37   $236.35   $236.40  
  Purchase #4 $38.93   7.854%   $41.9876   $41.99   $42.00   $42.00  
  Purchase #5 $116.53   6.346%   $123.925   $123.93   $123.95   $123.90  
  Purchase #6 $184.98   12.112%   $207.3848   $207.38   $207.40   $207.40  
  Purchase #7 $54.74   13.167%   $61.9476   $61.95   $61.95   $61.90  
  7 purchase totals = $872.26       $945.9715   $945.98   $946.00   $946.00