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 $98.76   7.849%   $106.5117   $106.51   $106.50   $106.50  
  Purchase #2 $217.47   11.197%   $241.8201   $241.82   $241.80   $241.80  
  Purchase #3 $151.36   13.448%   $171.7149   $171.71   $171.70   $171.70  
  Purchase #4 $154.80   5.807%   $163.7892   $163.79   $163.80   $163.80  
  Purchase #5 $119.87   5.294%   $126.2159   $126.22   $126.20   $126.20  
  Purchase #6 $174.33   4.870%   $182.8199   $182.82   $182.80   $182.80  
  Purchase #7 $34.53   5.206%   $36.3276   $36.33   $36.35   $36.30  
  7 purchase totals = $951.12       $1,029.1993   $1,029.20   $1,029.15   $1,029.10