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 $181.96   13.316%   $206.1898   $206.19   $206.20   $206.20  
  Purchase #2 $190.39   3.792%   $197.6096   $197.61   $197.60   $197.60  
  Purchase #3 $58.45   13.274%   $66.2087   $66.21   $66.20   $66.20  
  Purchase #4 $26.34   7.261%   $28.2525   $28.25   $28.25   $28.30  
  Purchase #5 $25.72   11.249%   $28.6132   $28.61   $28.60   $28.60  
  Purchase #6 $44.43   6.780%   $47.4424   $47.44   $47.45   $47.40  
  Purchase #7 $155.25   13.694%   $176.5099   $176.51   $176.50   $176.50  
  7 purchase totals = $682.54       $750.8261   $750.82   $750.80   $750.80