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 $31.46   9.161%   $34.3421   $34.34   $34.35   $34.30  
  Purchase #2 $115.52   6.175%   $122.6534   $122.65   $122.65   $122.70  
  Purchase #3 $19.39   5.722%   $20.4995   $20.50   $20.50   $20.50  
  Purchase #4 $156.34   3.409%   $161.6696   $161.67   $161.65   $161.70  
  Purchase #5 $175.88   12.354%   $197.6082   $197.61   $197.60   $197.60  
  Purchase #6 $153.84   6.785%   $164.278   $164.28   $164.30   $164.30  
  Purchase #7 $114.93   10.660%   $127.1815   $127.18   $127.20   $127.20  
  7 purchase totals = $767.36       $828.2323   $828.23   $828.25   $828.30