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 $35.30   8.195%   $38.1928   $38.19   $38.20   $38.20  
  Purchase #2 $190.99   5.818%   $202.1018   $202.10   $202.10   $202.10  
  Purchase #3 $10.65   6.387%   $11.3302   $11.33   $11.35   $11.30  
  Purchase #4 $118.75   5.694%   $125.5116   $125.51   $125.50   $125.50  
  Purchase #5 $222.56   7.491%   $239.232   $239.23   $239.25   $239.20  
  Purchase #6 $171.87   8.435%   $186.3672   $186.37   $186.35   $186.40  
  Purchase #7 $245.34   5.681%   $259.2778   $259.28   $259.30   $259.30  
  7 purchase totals = $995.46       $1,062.0134   $1,062.01   $1,062.05   $1,062.00