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 $116.79   5.548%   $123.2695   $123.27   $123.25   $123.30  
  Purchase #2 $227.58   5.327%   $239.7032   $239.70   $239.70   $239.70  
  Purchase #3 $26.67   13.457%   $30.259   $30.26   $30.25   $30.30  
  Purchase #4 $59.71   13.727%   $67.9064   $67.91   $67.90   $67.90  
  Purchase #5 $57.92   12.589%   $65.2115   $65.21   $65.20   $65.20  
  Purchase #6 $246.43   9.575%   $270.0257   $270.03   $270.05   $270.00  
  Purchase #7 $57.58   13.224%   $65.1944   $65.19   $65.20   $65.20  
  7 purchase totals = $792.68       $861.5697   $861.57   $861.55   $861.60