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 $46.89   12.512%   $52.7569   $52.76   $52.75   $52.80  
  Purchase #2 $117.86   8.249%   $127.5823   $127.58   $127.60   $127.60  
  Purchase #3 $80.36   9.422%   $87.9315   $87.93   $87.95   $87.90  
  Purchase #4 $95.41   8.188%   $103.2222   $103.22   $103.20   $103.20  
  Purchase #5 $186.61   5.617%   $197.0919   $197.09   $197.10   $197.10  
  Purchase #6 $149.43   9.385%   $163.454   $163.45   $163.45   $163.50  
  Purchase #7 $203.83   13.736%   $231.8281   $231.83   $231.85   $231.80  
  7 purchase totals = $880.39       $963.8669   $963.86   $963.90   $963.90