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 $65.40   9.851%   $71.8426   $71.84   $71.85   $71.80  
  Purchase #2 $77.25   12.158%   $86.6421   $86.64   $86.65   $86.60  
  Purchase #3 $103.95   11.722%   $116.135   $116.14   $116.15   $116.10  
  Purchase #4 $156.66   7.155%   $167.869   $167.87   $167.85   $167.90  
  Purchase #5 $55.49   3.158%   $57.2424   $57.24   $57.25   $57.20  
  Purchase #6 $213.75   12.410%   $240.2764   $240.28   $240.30   $240.30  
  Purchase #7 $217.42   6.776%   $232.1524   $232.15   $232.15   $232.20  
  7 purchase totals = $889.92       $972.1599   $972.16   $972.20   $972.10