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 $135.93   6.113%   $144.2394   $144.24   $144.25   $144.20  
  Purchase #2 $226.91   5.695%   $239.8325   $239.83   $239.85   $239.80  
  Purchase #3 $14.53   10.250%   $16.0193   $16.02   $16.00   $16.00  
  Purchase #4 $89.59   11.181%   $99.6071   $99.61   $99.60   $99.60  
  Purchase #5 $167.55   11.771%   $187.2723   $187.27   $187.25   $187.30  
  Purchase #6 $22.44   8.311%   $24.305   $24.31   $24.30   $24.30  
  Purchase #7 $26.26   13.421%   $29.7844   $29.78   $29.80   $29.80  
  7 purchase totals = $683.21       $741.0600   $741.06   $741.05   $741.00