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 $170.86   12.675%   $192.5165   $192.52   $192.50   $192.50  
  Purchase #2 $173.41   3.413%   $179.3285   $179.33   $179.35   $179.30  
  Purchase #3 $203.99   3.517%   $211.1643   $211.16   $211.15   $211.20  
  Purchase #4 $163.52   11.430%   $182.2103   $182.21   $182.20   $182.20  
  Purchase #5 $96.63   7.151%   $103.54   $103.54   $103.55   $103.50  
  Purchase #6 $234.27   3.280%   $241.9541   $241.95   $241.95   $242.00  
  Purchase #7 $161.48   6.260%   $171.5886   $171.59   $171.60   $171.60  
  7 purchase totals = $1,204.16       $1,282.3023   $1,282.30   $1,282.30   $1,282.30