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 $84.49   11.735%   $94.4049   $94.40   $94.40   $94.40  
  Purchase #2 $24.83   5.659%   $26.2351   $26.24   $26.25   $26.20  
  Purchase #3 $206.89   10.461%   $228.5328   $228.53   $228.55   $228.50  
  Purchase #4 $117.51   11.355%   $130.8533   $130.85   $130.85   $130.90  
  Purchase #5 $179.79   3.129%   $185.4156   $185.42   $185.40   $185.40  
  Purchase #6 $177.51   4.568%   $185.6187   $185.62   $185.60   $185.60  
  Purchase #7 $207.83   4.744%   $217.6895   $217.69   $217.70   $217.70  
  7 purchase totals = $998.85       $1,068.7499   $1,068.75   $1,068.75   $1,068.70