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 $173.83   13.202%   $196.779   $196.78   $196.80   $196.80  
  Purchase #2 $28.81   13.519%   $32.7048   $32.70   $32.70   $32.70  
  Purchase #3 $131.90   3.862%   $136.994   $136.99   $137.00   $137.00  
  Purchase #4 $243.49   12.509%   $273.9482   $273.95   $273.95   $273.90  
  Purchase #5 $172.35   6.218%   $183.0667   $183.07   $183.05   $183.10  
  Purchase #6 $120.87   4.438%   $126.2342   $126.23   $126.25   $126.20  
  Purchase #7 $24.62   11.865%   $27.5412   $27.54   $27.55   $27.50  
  7 purchase totals = $895.87       $977.2681   $977.26   $977.30   $977.20