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 $115.94   9.740%   $127.2326   $127.23   $127.25   $127.20  
  Purchase #2 $195.73   3.430%   $202.4435   $202.44   $202.45   $202.40  
  Purchase #3 $70.81   8.754%   $77.0087   $77.01   $77.00   $77.00  
  Purchase #4 $7.45   10.774%   $8.2527   $8.25   $8.25   $8.30  
  Purchase #5 $234.93   9.301%   $256.7808   $256.78   $256.80   $256.80  
  Purchase #6 $78.32   10.604%   $86.6251   $86.63   $86.65   $86.60  
  Purchase #7 $70.44   7.657%   $75.8336   $75.83   $75.85   $75.80  
  7 purchase totals = $773.62       $834.1770   $834.17   $834.25   $834.10