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 $63.67   5.359%   $67.0821   $67.08   $67.10   $67.10  
  Purchase #2 $205.45   13.422%   $233.0255   $233.03   $233.05   $233.00  
  Purchase #3 $79.72   12.510%   $89.693   $89.69   $89.70   $89.70  
  Purchase #4 $162.99   7.855%   $175.7929   $175.79   $175.80   $175.80  
  Purchase #5 $244.70   5.394%   $257.8991   $257.90   $257.90   $257.90  
  Purchase #6 $36.58   7.289%   $39.2463   $39.25   $39.25   $39.20  
  Purchase #7 $131.58   3.333%   $135.9656   $135.97   $135.95   $136.00  
  7 purchase totals = $924.69       $998.7045   $998.71   $998.75   $998.70