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 $203.98   4.131%   $212.4064   $212.41   $212.40   $212.40  
  Purchase #2 $89.66   5.247%   $94.3645   $94.36   $94.35   $94.40  
  Purchase #3 $44.62   13.695%   $50.7307   $50.73   $50.75   $50.70  
  Purchase #4 $213.33   4.852%   $223.6808   $223.68   $223.70   $223.70  
  Purchase #5 $99.51   13.569%   $113.0125   $113.01   $113.00   $113.00  
  Purchase #6 $224.53   9.521%   $245.9075   $245.91   $245.90   $245.90  
  Purchase #7 $82.91   7.668%   $89.2675   $89.27   $89.25   $89.30  
  7 purchase totals = $958.54       $1,029.3699   $1,029.37   $1,029.35   $1,029.40