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 $186.81   10.813%   $207.0098   $207.01   $207.00   $207.00  
  Purchase #2 $242.50   5.830%   $256.6378   $256.64   $256.65   $256.60  
  Purchase #3 $96.69   6.551%   $103.0242   $103.02   $103.00   $103.00  
  Purchase #4 $227.37   7.276%   $243.9134   $243.91   $243.90   $243.90  
  Purchase #5 $208.40   5.678%   $220.233   $220.23   $220.25   $220.20  
  Purchase #6 $239.60   6.219%   $254.5007   $254.50   $254.50   $254.50  
  Purchase #7 $126.46   5.642%   $133.5949   $133.59   $133.60   $133.60  
  7 purchase totals = $1,327.83       $1,418.9138   $1,418.90   $1,418.90   $1,418.80