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 $47.37   8.804%   $51.5405   $51.54   $51.55   $51.50  
  Purchase #2 $243.92   10.286%   $269.0096   $269.01   $269.00   $269.00  
  Purchase #3 $90.37   5.427%   $95.2744   $95.27   $95.25   $95.30  
  Purchase #4 $60.85   6.370%   $64.7261   $64.73   $64.75   $64.70  
  Purchase #5 $211.73   13.312%   $239.9155   $239.92   $239.90   $239.90  
  Purchase #6 $142.88   12.563%   $160.83   $160.83   $160.85   $160.80  
  Purchase #7 $175.32   11.334%   $195.1908   $195.19   $195.20   $195.20  
  7 purchase totals = $972.44       $1,076.4869   $1,076.49   $1,076.50   $1,076.40