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 $97.85   6.628%   $104.3355   $104.34   $104.35   $104.30  
  Purchase #2 $88.93   3.395%   $91.9492   $91.95   $91.95   $91.90  
  Purchase #3 $5.37   3.435%   $5.5545   $5.55   $5.55   $5.60  
  Purchase #4 $174.88   3.660%   $181.2806   $181.28   $181.30   $181.30  
  Purchase #5 $191.93   12.491%   $215.904   $215.90   $215.90   $215.90  
  Purchase #6 $153.79   7.146%   $164.7798   $164.78   $164.80   $164.80  
  Purchase #7 $157.60   11.670%   $175.9919   $175.99   $176.00   $176.00  
  7 purchase totals = $870.35       $939.7955   $939.79   $939.85   $939.80