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 $159.40   6.414%   $169.6239   $169.62   $169.60   $169.60  
  Purchase #2 $237.46   10.609%   $262.6521   $262.65   $262.65   $262.70  
  Purchase #3 $148.77   7.280%   $159.6005   $159.60   $159.60   $159.60  
  Purchase #4 $69.58   3.581%   $72.0717   $72.07   $72.05   $72.10  
  Purchase #5 $19.61   13.563%   $22.2697   $22.27   $22.25   $22.30  
  Purchase #6 $201.62   10.856%   $223.5079   $223.51   $223.50   $223.50  
  Purchase #7 $24.77   6.528%   $26.387   $26.39   $26.40   $26.40  
  7 purchase totals = $861.21       $936.1128   $936.11   $936.05   $936.20