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 $248.99   11.130%   $276.7026   $276.70   $276.70   $276.70  
  Purchase #2 $195.79   9.608%   $214.6015   $214.60   $214.60   $214.60  
  Purchase #3 $5.87   7.117%   $6.2878   $6.29   $6.30   $6.30  
  Purchase #4 $135.88   12.320%   $152.6204   $152.62   $152.60   $152.60  
  Purchase #5 $205.44   3.206%   $212.0264   $212.03   $212.05   $212.00  
  Purchase #6 $124.42   10.833%   $137.8984   $137.90   $137.90   $137.90  
  Purchase #7 $144.26   9.743%   $158.3153   $158.32   $158.30   $158.30  
  7 purchase totals = $1,060.65       $1,158.4524   $1,158.46   $1,158.45   $1,158.40