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 $54.74   10.700%   $60.5972   $60.60   $60.60   $60.60  
  Purchase #2 $43.86   6.421%   $46.6763   $46.68   $46.70   $46.70  
  Purchase #3 $239.27   8.214%   $258.9236   $258.92   $258.90   $258.90  
  Purchase #4 $131.51   7.566%   $141.46   $141.46   $141.45   $141.50  
  Purchase #5 $227.49   9.454%   $248.9969   $249.00   $249.00   $249.00  
  Purchase #6 $68.45   8.249%   $74.0964   $74.10   $74.10   $74.10  
  Purchase #7 $34.66   4.798%   $36.323   $36.32   $36.30   $36.30  
  7 purchase totals = $799.98       $867.0734   $867.08   $867.05   $867.10