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 $86.69   11.377%   $96.5527   $96.55   $96.55   $96.60  
  Purchase #2 $127.38   6.789%   $136.0278   $136.03   $136.05   $136.00  
  Purchase #3 $240.59   11.384%   $267.9788   $267.98   $268.00   $268.00  
  Purchase #4 $102.51   8.384%   $111.1044   $111.10   $111.10   $111.10  
  Purchase #5 $61.89   6.717%   $66.0472   $66.05   $66.05   $66.00  
  Purchase #6 $23.84   9.162%   $26.0242   $26.02   $26.00   $26.00  
  Purchase #7 $131.91   6.717%   $140.7704   $140.77   $140.75   $140.80  
  7 purchase totals = $774.81       $844.5055   $844.50   $844.50   $844.50