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 $56.61   9.796%   $62.1555   $62.16   $62.15   $62.20  
  Purchase #2 $153.26   7.274%   $164.4081   $164.41   $164.40   $164.40  
  Purchase #3 $198.90   7.145%   $213.1114   $213.11   $213.10   $213.10  
  Purchase #4 $76.94   10.655%   $85.138   $85.14   $85.15   $85.10  
  Purchase #5 $65.39   13.436%   $74.1758   $74.18   $74.20   $74.20  
  Purchase #6 $133.49   6.276%   $141.8678   $141.87   $141.85   $141.90  
  Purchase #7 $245.69   7.584%   $264.3231   $264.32   $264.30   $264.30  
  7 purchase totals = $930.28       $1,005.1797   $1,005.19   $1,005.15   $1,005.20