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 $51.26   7.646%   $55.1793   $55.18   $55.20   $55.20  
  Purchase #2 $150.46   9.592%   $164.8921   $164.89   $164.90   $164.90  
  Purchase #3 $221.33   5.500%   $233.5032   $233.50   $233.50   $233.50  
  Purchase #4 $80.66   4.561%   $84.3389   $84.34   $84.35   $84.30  
  Purchase #5 $24.84   10.143%   $27.3595   $27.36   $27.35   $27.40  
  Purchase #6 $58.85   6.219%   $62.5099   $62.51   $62.50   $62.50  
  Purchase #7 $163.51   7.166%   $175.2271   $175.23   $175.25   $175.20  
  7 purchase totals = $750.91       $803.0100   $803.01   $803.05   $803.00