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 $88.90   10.832%   $98.5296   $98.53   $98.55   $98.50  
  Purchase #2 $158.49   9.826%   $174.0632   $174.06   $174.05   $174.10  
  Purchase #3 $225.40   7.142%   $241.4981   $241.50   $241.50   $241.50  
  Purchase #4 $153.80   8.444%   $166.7869   $166.79   $166.80   $166.80  
  Purchase #5 $166.53   6.603%   $177.526   $177.53   $177.55   $177.50  
  Purchase #6 $116.67   9.104%   $127.2916   $127.29   $127.30   $127.30  
  Purchase #7 $250.95   10.762%   $277.9572   $277.96   $277.95   $278.00  
  7 purchase totals = $1,160.74       $1,263.6526   $1,263.66   $1,263.70   $1,263.70