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 $96.95   6.347%   $103.1034   $103.10   $103.10   $103.10  
  Purchase #2 $237.58   10.294%   $262.0365   $262.04   $262.05   $262.00  
  Purchase #3 $197.38   7.143%   $211.4789   $211.48   $211.50   $211.50  
  Purchase #4 $47.63   12.295%   $53.4861   $53.49   $53.50   $53.50  
  Purchase #5 $183.55   6.307%   $195.1265   $195.13   $195.15   $195.10  
  Purchase #6 $217.53   11.395%   $242.3175   $242.32   $242.30   $242.30  
  Purchase #7 $238.46   8.553%   $258.8555   $258.86   $258.85   $258.90  
  7 purchase totals = $1,219.08       $1,326.4044   $1,326.42   $1,326.45   $1,326.40