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 $71.44   5.343%   $75.257   $75.26   $75.25   $75.30  
  Purchase #2 $169.59   9.830%   $186.2607   $186.26   $186.25   $186.30  
  Purchase #3 $72.72   5.560%   $76.7632   $76.76   $76.75   $76.80  
  Purchase #4 $125.45   4.777%   $131.4427   $131.44   $131.45   $131.40  
  Purchase #5 $119.73   5.114%   $125.853   $125.85   $125.85   $125.90  
  Purchase #6 $122.44   6.223%   $130.0594   $130.06   $130.05   $130.10  
  Purchase #7 $165.86   9.279%   $181.2501   $181.25   $181.25   $181.30  
  7 purchase totals = $847.23       $906.8861   $906.88   $906.85   $907.10