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 $51.49   12.730%   $58.0447   $58.04   $58.05   $58.00  
  Purchase #2 $241.80   8.615%   $262.6311   $262.63   $262.65   $262.60  
  Purchase #3 $87.90   11.391%   $97.9127   $97.91   $97.90   $97.90  
  Purchase #4 $235.39   3.493%   $243.6122   $243.61   $243.60   $243.60  
  Purchase #5 $86.39   7.566%   $92.9263   $92.93   $92.95   $92.90  
  Purchase #6 $215.56   9.221%   $235.4368   $235.44   $235.45   $235.40  
  Purchase #7 $109.57   7.789%   $118.1044   $118.10   $118.10   $118.10  
  7 purchase totals = $1,028.10       $1,108.6682   $1,108.66   $1,108.70   $1,108.50