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 $242.99   9.510%   $266.0983   $266.10   $266.10   $266.10  
  Purchase #2 $137.68   7.275%   $147.6962   $147.70   $147.70   $147.70  
  Purchase #3 $220.58   13.373%   $250.0782   $250.08   $250.10   $250.10  
  Purchase #4 $243.50   12.462%   $273.845   $273.85   $273.85   $273.80  
  Purchase #5 $96.76   8.550%   $105.033   $105.03   $105.05   $105.00  
  Purchase #6 $184.76   6.202%   $196.2188   $196.22   $196.20   $196.20  
  Purchase #7 $113.33   7.505%   $121.8354   $121.84   $121.85   $121.80  
  7 purchase totals = $1,239.60       $1,360.8049   $1,360.82   $1,360.85   $1,360.70