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 $80.69   5.448%   $85.086   $85.09   $85.10   $85.10  
  Purchase #2 $13.34   8.783%   $14.5117   $14.51   $14.50   $14.50  
  Purchase #3 $73.38   10.146%   $80.8251   $80.83   $80.85   $80.80  
  Purchase #4 $226.59   6.742%   $241.8667   $241.87   $241.85   $241.90  
  Purchase #5 $144.42   4.288%   $150.6127   $150.61   $150.60   $150.60  
  Purchase #6 $160.91   4.343%   $167.8983   $167.90   $167.90   $167.90  
  Purchase #7 $157.60   12.436%   $177.1991   $177.20   $177.20   $177.20  
  7 purchase totals = $856.93       $917.9996   $918.01   $918.00   $918.00