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 $87.72   7.691%   $94.4665   $94.47   $94.45   $94.50  
  Purchase #2 $171.48   3.103%   $176.801   $176.80   $176.80   $176.80  
  Purchase #3 $155.57   6.349%   $165.4471   $165.45   $165.45   $165.40  
  Purchase #4 $247.72   8.684%   $269.232   $269.23   $269.25   $269.20  
  Purchase #5 $246.49   9.583%   $270.1111   $270.11   $270.10   $270.10  
  Purchase #6 $115.88   5.540%   $122.2998   $122.30   $122.30   $122.30  
  Purchase #7 $153.95   8.484%   $167.0111   $167.01   $167.00   $167.00  
  7 purchase totals = $1,178.81       $1,265.3686   $1,265.37   $1,265.35   $1,265.30