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 $224.87   9.207%   $245.5738   $245.57   $245.55   $245.60  
  Purchase #2 $51.68   9.244%   $56.4573   $56.46   $56.45   $56.50  
  Purchase #3 $53.98   7.313%   $57.9276   $57.93   $57.95   $57.90  
  Purchase #4 $148.49   6.630%   $158.3349   $158.33   $158.35   $158.30  
  Purchase #5 $20.52   3.444%   $21.2267   $21.23   $21.25   $21.20  
  Purchase #6 $248.36   10.361%   $274.0926   $274.09   $274.10   $274.10  
  Purchase #7 $210.25   8.448%   $228.0119   $228.01   $228.00   $228.00  
  7 purchase totals = $958.15       $1,041.6248   $1,041.62   $1,041.65   $1,041.60