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 $50.71   4.355%   $52.9184   $52.92   $52.90   $52.90  
  Purchase #2 $184.98   3.833%   $192.0703   $192.07   $192.05   $192.10  
  Purchase #3 $230.72   5.838%   $244.1894   $244.19   $244.20   $244.20  
  Purchase #4 $53.72   7.581%   $57.7925   $57.79   $57.80   $57.80  
  Purchase #5 $237.33   10.116%   $261.3383   $261.34   $261.35   $261.30  
  Purchase #6 $175.52   4.650%   $183.6817   $183.68   $183.70   $183.70  
  Purchase #7 $20.51   12.340%   $23.0409   $23.04   $23.05   $23.00  
  7 purchase totals = $953.49       $1,015.0315   $1,015.03   $1,015.05   $1,015.00