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 $12.65   13.128%   $14.3107   $14.31   $14.30   $14.30  
  Purchase #2 $30.88   3.465%   $31.95   $31.95   $31.95   $32.00  
  Purchase #3 $97.91   7.243%   $105.0016   $105.00   $105.00   $105.00  
  Purchase #4 $66.83   11.820%   $74.7293   $74.73   $74.75   $74.70  
  Purchase #5 $93.59   5.639%   $98.8675   $98.87   $98.85   $98.90  
  Purchase #6 $202.91   4.182%   $211.3957   $211.40   $211.40   $211.40  
  Purchase #7 $159.64   11.633%   $178.2109   $178.21   $178.20   $178.20  
  7 purchase totals = $664.41       $714.4657   $714.47   $714.45   $714.50