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 $198.48   4.373%   $207.1595   $207.16   $207.15   $207.20  
  Purchase #2 $158.72   11.284%   $176.63   $176.63   $176.65   $176.60  
  Purchase #3 $67.97   8.582%   $73.8032   $73.80   $73.80   $73.80  
  Purchase #4 $33.35   8.258%   $36.104   $36.10   $36.10   $36.10  
  Purchase #5 $237.54   12.402%   $266.9997   $267.00   $267.00   $267.00  
  Purchase #6 $87.82   12.273%   $98.5981   $98.60   $98.60   $98.60  
  Purchase #7 $52.39   7.104%   $56.1118   $56.11   $56.10   $56.10  
  7 purchase totals = $836.27       $915.4063   $915.40   $915.40   $915.40