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 $34.36   9.616%   $37.6641   $37.66   $37.65   $37.70  
  Purchase #2 $186.76   11.391%   $208.0338   $208.03   $208.05   $208.00  
  Purchase #3 $154.42   7.846%   $166.5358   $166.54   $166.55   $166.50  
  Purchase #4 $192.59   6.465%   $205.0409   $205.04   $205.05   $205.00  
  Purchase #5 $222.72   4.279%   $232.2502   $232.25   $232.25   $232.30  
  Purchase #6 $183.57   4.159%   $191.2047   $191.20   $191.20   $191.20  
  Purchase #7 $14.62   10.430%   $16.1449   $16.14   $16.15   $16.10  
  7 purchase totals = $989.04       $1,056.8744   $1,056.86   $1,056.90   $1,056.80