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 $208.55   12.412%   $234.4352   $234.44   $234.45   $234.40  
  Purchase #2 $91.79   4.798%   $96.1941   $96.19   $96.20   $96.20  
  Purchase #3 $84.33   10.640%   $93.3027   $93.30   $93.30   $93.30  
  Purchase #4 $127.79   7.693%   $137.6209   $137.62   $137.60   $137.60  
  Purchase #5 $166.44   11.212%   $185.1013   $185.10   $185.10   $185.10  
  Purchase #6 $193.38   5.288%   $203.6059   $203.61   $203.60   $203.60  
  Purchase #7 $246.71   12.444%   $277.4106   $277.41   $277.40   $277.40  
  7 purchase totals = $1,118.99       $1,227.6707   $1,227.67   $1,227.65   $1,227.60