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 $233.85   11.715%   $261.2455   $261.25   $261.25   $261.20  
  Purchase #2 $191.72   11.273%   $213.3326   $213.33   $213.35   $213.30  
  Purchase #3 $190.81   13.266%   $216.1229   $216.12   $216.10   $216.10  
  Purchase #4 $246.88   3.258%   $254.9234   $254.92   $254.90   $254.90  
  Purchase #5 $208.38   8.305%   $225.686   $225.69   $225.70   $225.70  
  Purchase #6 $201.56   5.512%   $212.67   $212.67   $212.65   $212.70  
  Purchase #7 $244.57   3.186%   $252.362   $252.36   $252.35   $252.40  
  7 purchase totals = $1,517.77       $1,636.3424   $1,636.34   $1,636.30   $1,636.30