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 $5.38   7.690%   $5.7937   $5.79   $5.80   $5.80  
  Purchase #2 $208.59   6.748%   $222.6657   $222.67   $222.65   $222.70  
  Purchase #3 $229.41   9.747%   $251.7706   $251.77   $251.75   $251.80  
  Purchase #4 $111.44   12.165%   $124.9967   $125.00   $125.00   $125.00  
  Purchase #5 $142.45   7.256%   $152.7862   $152.79   $152.80   $152.80  
  Purchase #6 $49.88   5.388%   $52.5675   $52.57   $52.55   $52.60  
  Purchase #7 $36.92   4.407%   $38.5471   $38.55   $38.55   $38.50  
  7 purchase totals = $784.07       $849.1275   $849.14   $849.10   $849.20