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 $37.94   9.373%   $41.4961   $41.50   $41.50   $41.50  
  Purchase #2 $101.80   6.324%   $108.2378   $108.24   $108.25   $108.20  
  Purchase #3 $124.36   12.521%   $139.9311   $139.93   $139.95   $139.90  
  Purchase #4 $179.88   13.405%   $203.9929   $203.99   $204.00   $204.00  
  Purchase #5 $178.98   7.365%   $192.1619   $192.16   $192.15   $192.20  
  Purchase #6 $195.94   5.369%   $206.46   $206.46   $206.45   $206.50  
  Purchase #7 $126.42   6.422%   $134.5387   $134.54   $134.55   $134.50  
  7 purchase totals = $945.32       $1,026.8185   $1,026.82   $1,026.85   $1,026.80