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 $181.31   8.459%   $196.647   $196.65   $196.65   $196.60  
  Purchase #2 $81.66   5.771%   $86.3726   $86.37   $86.35   $86.40  
  Purchase #3 $249.41   9.846%   $273.9669   $273.97   $273.95   $274.00  
  Purchase #4 $140.48   10.426%   $155.1264   $155.13   $155.15   $155.10  
  Purchase #5 $242.97   4.554%   $254.0349   $254.03   $254.05   $254.00  
  Purchase #6 $156.87   5.271%   $165.1386   $165.14   $165.15   $165.10  
  Purchase #7 $113.98   10.546%   $126.0003   $126.00   $126.00   $126.00  
  7 purchase totals = $1,166.68       $1,257.2867   $1,257.29   $1,257.30   $1,257.20