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 $41.27   8.239%   $44.6702   $44.67   $44.65   $44.70  
  Purchase #2 $108.45   12.607%   $122.1223   $122.12   $122.10   $122.10  
  Purchase #3 $152.26   13.441%   $172.7253   $172.73   $172.75   $172.70  
  Purchase #4 $208.98   7.671%   $225.0109   $225.01   $225.00   $225.00  
  Purchase #5 $130.96   12.438%   $147.2488   $147.25   $147.25   $147.20  
  Purchase #6 $243.43   6.659%   $259.64   $259.64   $259.65   $259.60  
  Purchase #7 $10.34   5.784%   $10.9381   $10.94   $10.95   $10.90  
  7 purchase totals = $895.69       $982.3556   $982.36   $982.35   $982.20