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 $68.66   8.670%   $74.6128   $74.61   $74.60   $74.60  
  Purchase #2 $22.81   9.656%   $25.0125   $25.01   $25.00   $25.00  
  Purchase #3 $230.35   6.451%   $245.2099   $245.21   $245.20   $245.20  
  Purchase #4 $154.80   13.258%   $175.3234   $175.32   $175.30   $175.30  
  Purchase #5 $29.91   6.670%   $31.905   $31.91   $31.90   $31.90  
  Purchase #6 $148.98   10.145%   $164.094   $164.09   $164.10   $164.10  
  Purchase #7 $117.71   4.563%   $123.0811   $123.08   $123.10   $123.10  
  7 purchase totals = $773.22       $839.2387   $839.23   $839.20   $839.20