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 $153.29   5.829%   $162.2253   $162.23   $162.25   $162.20  
  Purchase #2 $243.92   10.151%   $268.6803   $268.68   $268.70   $268.70  
  Purchase #3 $217.93   6.675%   $232.4768   $232.48   $232.50   $232.50  
  Purchase #4 $34.99   8.829%   $38.0793   $38.08   $38.10   $38.10  
  Purchase #5 $38.50   13.157%   $43.5654   $43.57   $43.55   $43.60  
  Purchase #6 $94.39   7.527%   $101.4947   $101.49   $101.50   $101.50  
  Purchase #7 $7.61   10.265%   $8.3912   $8.39   $8.40   $8.40  
  7 purchase totals = $790.63       $854.9130   $854.92   $855.00   $855.00