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 $241.96   10.677%   $267.7941   $267.79   $267.80   $267.80  
  Purchase #2 $58.66   8.405%   $63.5904   $63.59   $63.60   $63.60  
  Purchase #3 $213.76   8.781%   $232.5303   $232.53   $232.55   $232.50  
  Purchase #4 $236.32   5.401%   $249.0836   $249.08   $249.10   $249.10  
  Purchase #5 $248.57   7.540%   $267.3122   $267.31   $267.30   $267.30  
  Purchase #6 $39.55   13.314%   $44.8157   $44.82   $44.80   $44.80  
  Purchase #7 $182.25   7.489%   $195.8987   $195.90   $195.90   $195.90  
  7 purchase totals = $1,221.07       $1,321.0250   $1,321.02   $1,321.05   $1,321.00