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 $41.41   12.808%   $46.7138   $46.71   $46.70   $46.70  
  Purchase #2 $52.73   6.126%   $55.9602   $55.96   $55.95   $56.00  
  Purchase #3 $96.83   6.292%   $102.9225   $102.92   $102.90   $102.90  
  Purchase #4 $185.35   9.749%   $203.4198   $203.42   $203.40   $203.40  
  Purchase #5 $183.42   7.763%   $197.6589   $197.66   $197.65   $197.70  
  Purchase #6 $66.69   5.338%   $70.2499   $70.25   $70.25   $70.20  
  Purchase #7 $174.67   10.497%   $193.0051   $193.01   $193.00   $193.00  
  7 purchase totals = $801.10       $869.9302   $869.93   $869.85   $869.90