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 $208.73   10.685%   $231.0328   $231.03   $231.05   $231.00  
  Purchase #2 $198.37   4.730%   $207.7529   $207.75   $207.75   $207.80  
  Purchase #3 $84.96   10.838%   $94.168   $94.17   $94.15   $94.20  
  Purchase #4 $82.61   3.293%   $85.3303   $85.33   $85.35   $85.30  
  Purchase #5 $12.65   9.581%   $13.862   $13.86   $13.85   $13.90  
  Purchase #6 $43.97   4.804%   $46.0823   $46.08   $46.10   $46.10  
  Purchase #7 $223.30   11.343%   $248.6289   $248.63   $248.65   $248.60  
  7 purchase totals = $854.59       $926.8572   $926.85   $926.90   $926.90