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 $86.77   13.581%   $98.5542   $98.55   $98.55   $98.60  
  Purchase #2 $245.70   8.378%   $266.2847   $266.28   $266.30   $266.30  
  Purchase #3 $13.89   8.267%   $15.0383   $15.04   $15.05   $15.00  
  Purchase #4 $232.58   6.578%   $247.8791   $247.88   $247.90   $247.90  
  Purchase #5 $95.56   12.523%   $107.527   $107.53   $107.55   $107.50  
  Purchase #6 $239.83   10.774%   $265.6693   $265.67   $265.65   $265.70  
  Purchase #7 $244.50   7.700%   $263.3265   $263.33   $263.35   $263.30  
  7 purchase totals = $1,158.83       $1,264.2791   $1,264.28   $1,264.35   $1,264.30