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 $35.61   3.595%   $36.8902   $36.89   $36.90   $36.90  
  Purchase #2 $212.28   8.770%   $230.897   $230.90   $230.90   $230.90  
  Purchase #3 $24.99   3.182%   $25.7852   $25.79   $25.80   $25.80  
  Purchase #4 $16.48   9.693%   $18.0774   $18.08   $18.10   $18.10  
  Purchase #5 $85.96   7.137%   $92.095   $92.10   $92.10   $92.10  
  Purchase #6 $182.51   7.196%   $195.6434   $195.64   $195.65   $195.60  
  Purchase #7 $30.88   13.675%   $35.1028   $35.10   $35.10   $35.10  
  7 purchase totals = $588.71       $634.4910   $634.50   $634.55   $634.50