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 $201.77   11.144%   $224.2552   $224.26   $224.25   $224.30  
  Purchase #2 $7.27   3.446%   $7.5205   $7.52   $7.50   $7.50  
  Purchase #3 $215.83   11.116%   $239.8217   $239.82   $239.80   $239.80  
  Purchase #4 $15.43   9.246%   $16.8567   $16.86   $16.85   $16.90  
  Purchase #5 $118.95   6.727%   $126.9518   $126.95   $126.95   $127.00  
  Purchase #6 $131.87   5.780%   $139.4921   $139.49   $139.50   $139.50  
  Purchase #7 $247.73   8.364%   $268.4501   $268.45   $268.45   $268.50  
  7 purchase totals = $938.85       $1,023.3481   $1,023.35   $1,023.30   $1,023.50