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 $34.27   3.667%   $35.5267   $35.53   $35.55   $35.50  
  Purchase #2 $230.55   10.513%   $254.7877   $254.79   $254.80   $254.80  
  Purchase #3 $188.42   8.790%   $204.9821   $204.98   $205.00   $205.00  
  Purchase #4 $174.97   6.460%   $186.2731   $186.27   $186.25   $186.30  
  Purchase #5 $231.27   8.631%   $251.2309   $251.23   $251.25   $251.20  
  Purchase #6 $60.47   7.608%   $65.0706   $65.07   $65.05   $65.10  
  Purchase #7 $32.62   6.147%   $34.6252   $34.63   $34.65   $34.60  
  7 purchase totals = $952.57       $1,032.4963   $1,032.50   $1,032.55   $1,032.50