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 $108.32   13.223%   $122.6432   $122.64   $122.65   $122.60  
  Purchase #2 $115.72   3.403%   $119.658   $119.66   $119.65   $119.70  
  Purchase #3 $16.53   7.853%   $17.8281   $17.83   $17.85   $17.80  
  Purchase #4 $176.51   9.594%   $193.4444   $193.44   $193.45   $193.40  
  Purchase #5 $22.77   6.823%   $24.3236   $24.32   $24.30   $24.30  
  Purchase #6 $154.93   10.588%   $171.334   $171.33   $171.35   $171.30  
  Purchase #7 $97.48   9.644%   $106.881   $106.88   $106.90   $106.90  
  7 purchase totals = $692.26       $756.1123   $756.10   $756.15   $756.00