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 $46.38   9.210%   $50.6516   $50.65   $50.65   $50.70  
  Purchase #2 $232.72   7.474%   $250.1135   $250.11   $250.10   $250.10  
  Purchase #3 $139.94   7.844%   $150.9169   $150.92   $150.90   $150.90  
  Purchase #4 $98.62   8.385%   $106.8893   $106.89   $106.90   $106.90  
  Purchase #5 $185.36   3.479%   $191.8087   $191.81   $191.80   $191.80  
  Purchase #6 $105.81   13.335%   $119.9198   $119.92   $119.90   $119.90  
  Purchase #7 $178.66   8.400%   $193.6674   $193.67   $193.65   $193.70  
  7 purchase totals = $987.49       $1,063.9672   $1,063.97   $1,063.90   $1,064.00