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 $249.38   6.246%   $264.9563   $264.96   $264.95   $265.00  
  Purchase #2 $157.90   9.713%   $173.2368   $173.24   $173.25   $173.20  
  Purchase #3 $29.77   10.795%   $32.9837   $32.98   $33.00   $33.00  
  Purchase #4 $224.25   7.314%   $240.6516   $240.65   $240.65   $240.70  
  Purchase #5 $39.81   6.312%   $42.3228   $42.32   $42.30   $42.30  
  Purchase #6 $247.36   10.367%   $273.0038   $273.00   $273.00   $273.00  
  Purchase #7 $78.48   10.402%   $86.6435   $86.64   $86.65   $86.60  
  7 purchase totals = $1,026.95       $1,113.7985   $1,113.79   $1,113.80   $1,113.80