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 $178.61   8.402%   $193.6168   $193.62   $193.60   $193.60  
  Purchase #2 $129.61   9.462%   $141.8737   $141.87   $141.85   $141.90  
  Purchase #3 $147.26   10.182%   $162.254   $162.25   $162.25   $162.30  
  Purchase #4 $66.64   4.451%   $69.6061   $69.61   $69.60   $69.60  
  Purchase #5 $26.87   7.827%   $28.9731   $28.97   $28.95   $29.00  
  Purchase #6 $76.65   12.864%   $86.5103   $86.51   $86.50   $86.50  
  Purchase #7 $113.58   4.281%   $118.4424   $118.44   $118.45   $118.40  
  7 purchase totals = $739.22       $801.2764   $801.27   $801.20   $801.30