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 $240.84   4.487%   $251.6465   $251.65   $251.65   $251.60  
  Purchase #2 $24.67   6.810%   $26.35   $26.35   $26.35   $26.40  
  Purchase #3 $167.60   10.701%   $185.5349   $185.53   $185.55   $185.50  
  Purchase #4 $80.55   4.412%   $84.1039   $84.10   $84.10   $84.10  
  Purchase #5 $65.70   7.175%   $70.414   $70.41   $70.40   $70.40  
  Purchase #6 $8.82   5.707%   $9.3234   $9.32   $9.30   $9.30  
  Purchase #7 $186.35   4.749%   $195.1998   $195.20   $195.20   $195.20  
  7 purchase totals = $774.53       $822.5725   $822.56   $822.55   $822.50