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 $58.27   7.648%   $62.7265   $62.73   $62.75   $62.70  
  Purchase #2 $32.50   3.412%   $33.6089   $33.61   $33.60   $33.60  
  Purchase #3 $87.49   9.835%   $96.0946   $96.09   $96.10   $96.10  
  Purchase #4 $13.79   4.738%   $14.4434   $14.44   $14.45   $14.40  
  Purchase #5 $207.42   3.339%   $214.3458   $214.35   $214.35   $214.30  
  Purchase #6 $111.68   8.739%   $121.4397   $121.44   $121.45   $121.40  
  Purchase #7 $8.46   9.400%   $9.2552   $9.26   $9.25   $9.30  
  7 purchase totals = $519.61       $551.9141   $551.92   $551.95   $551.80