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 $80.56   6.393%   $85.7102   $85.71   $85.70   $85.70  
  Purchase #2 $84.69   9.393%   $92.6449   $92.64   $92.65   $92.60  
  Purchase #3 $170.83   13.162%   $193.3146   $193.31   $193.30   $193.30  
  Purchase #4 $165.94   11.561%   $185.1243   $185.12   $185.10   $185.10  
  Purchase #5 $93.30   11.780%   $104.2907   $104.29   $104.30   $104.30  
  Purchase #6 $173.71   11.335%   $193.4   $193.40   $193.40   $193.40  
  Purchase #7 $168.67   13.670%   $191.7272   $191.73   $191.75   $191.70  
  7 purchase totals = $937.70       $1,046.2119   $1,046.20   $1,046.20   $1,046.10