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 $226.88   6.220%   $240.9919   $240.99   $241.00   $241.00  
  Purchase #2 $26.49   3.440%   $27.4013   $27.40   $27.40   $27.40  
  Purchase #3 $86.64   11.382%   $96.5014   $96.50   $96.50   $96.50  
  Purchase #4 $82.57   5.863%   $87.4111   $87.41   $87.40   $87.40  
  Purchase #5 $122.57   8.488%   $132.9737   $132.97   $132.95   $133.00  
  Purchase #6 $155.73   6.478%   $165.8182   $165.82   $165.80   $165.80  
  Purchase #7 $217.30   7.688%   $234.006   $234.01   $234.00   $234.00  
  7 purchase totals = $918.18       $985.1036   $985.10   $985.05   $985.10