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 $34.84   9.175%   $38.0366   $38.04   $38.05   $38.00  
  Purchase #2 $137.74   13.544%   $156.3955   $156.40   $156.40   $156.40  
  Purchase #3 $114.89   7.126%   $123.0771   $123.08   $123.10   $123.10  
  Purchase #4 $165.81   7.191%   $177.7334   $177.73   $177.75   $177.70  
  Purchase #5 $119.96   8.844%   $130.5693   $130.57   $130.55   $130.60  
  Purchase #6 $197.27   5.713%   $208.54   $208.54   $208.55   $208.50  
  Purchase #7 $140.52   13.849%   $159.9806   $159.98   $160.00   $160.00  
  7 purchase totals = $911.03       $994.3325   $994.34   $994.40   $994.30