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 $48.29   13.463%   $54.7913   $54.79   $54.80   $54.80  
  Purchase #2 $110.84   10.692%   $122.691   $122.69   $122.70   $122.70  
  Purchase #3 $86.99   8.716%   $94.572   $94.57   $94.55   $94.60  
  Purchase #4 $111.38   3.294%   $115.0489   $115.05   $115.05   $115.00  
  Purchase #5 $183.69   3.135%   $189.4487   $189.45   $189.45   $189.40  
  Purchase #6 $127.57   4.255%   $132.9981   $133.00   $133.00   $133.00  
  Purchase #7 $78.35   5.194%   $82.4195   $82.42   $82.40   $82.40  
  7 purchase totals = $747.11       $791.9695   $791.97   $791.95   $791.90