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 $232.75   6.426%   $247.7065   $247.71   $247.70   $247.70  
  Purchase #2 $156.56   12.393%   $175.9625   $175.96   $175.95   $176.00  
  Purchase #3 $154.77   6.622%   $165.0189   $165.02   $165.00   $165.00  
  Purchase #4 $16.65   12.661%   $18.7581   $18.76   $18.75   $18.80  
  Purchase #5 $56.87   6.188%   $60.3891   $60.39   $60.40   $60.40  
  Purchase #6 $189.88   12.180%   $213.0074   $213.01   $213.00   $213.00  
  Purchase #7 $171.80   13.667%   $195.2799   $195.28   $195.30   $195.30  
  7 purchase totals = $979.28       $1,076.1224   $1,076.13   $1,076.10   $1,076.20