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 $64.36   10.671%   $71.2279   $71.23   $71.25   $71.20  
  Purchase #2 $115.76   9.515%   $126.7746   $126.77   $126.75   $126.80  
  Purchase #3 $147.30   13.666%   $167.43   $167.43   $167.45   $167.40  
  Purchase #4 $121.97   7.549%   $131.1775   $131.18   $131.20   $131.20  
  Purchase #5 $208.94   12.599%   $235.2644   $235.26   $235.25   $235.30  
  Purchase #6 $39.73   5.394%   $41.873   $41.87   $41.85   $41.90  
  Purchase #7 $73.44   10.553%   $81.1901   $81.19   $81.20   $81.20  
  7 purchase totals = $771.50       $854.9375   $854.93   $854.95   $855.00