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 $211.62   8.697%   $230.0246   $230.02   $230.00   $230.00  
  Purchase #2 $168.57   4.132%   $175.5353   $175.54   $175.55   $175.50  
  Purchase #3 $55.36   13.482%   $62.8236   $62.82   $62.80   $62.80  
  Purchase #4 $183.83   6.207%   $195.2403   $195.24   $195.25   $195.20  
  Purchase #5 $166.83   10.238%   $183.9101   $183.91   $183.90   $183.90  
  Purchase #6 $50.83   10.270%   $56.0502   $56.05   $56.05   $56.10  
  Purchase #7 $130.62   6.481%   $139.0855   $139.09   $139.10   $139.10  
  7 purchase totals = $967.66       $1,042.6696   $1,042.67   $1,042.65   $1,042.60