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 $205.43   13.707%   $233.5883   $233.59   $233.60   $233.60  
  Purchase #2 $192.68   8.195%   $208.4701   $208.47   $208.45   $208.50  
  Purchase #3 $110.91   10.425%   $122.4724   $122.47   $122.45   $122.50  
  Purchase #4 $175.88   9.344%   $192.3142   $192.31   $192.30   $192.30  
  Purchase #5 $31.89   8.216%   $34.5101   $34.51   $34.50   $34.50  
  Purchase #6 $70.30   4.506%   $73.4677   $73.47   $73.45   $73.50  
  Purchase #7 $148.86   7.574%   $160.1347   $160.13   $160.15   $160.10  
  7 purchase totals = $935.95       $1,024.9575   $1,024.95   $1,024.90   $1,025.00