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 $192.35   4.255%   $200.5345   $200.53   $200.55   $200.50  
  Purchase #2 $38.94   10.413%   $42.9948   $42.99   $43.00   $43.00  
  Purchase #3 $249.88   8.652%   $271.4996   $271.50   $271.50   $271.50  
  Purchase #4 $83.46   12.124%   $93.5787   $93.58   $93.60   $93.60  
  Purchase #5 $118.45   13.145%   $134.0203   $134.02   $134.00   $134.00  
  Purchase #6 $180.27   8.774%   $196.0869   $196.09   $196.10   $196.10  
  Purchase #7 $243.26   13.863%   $276.9831   $276.98   $277.00   $277.00  
  7 purchase totals = $1,106.61       $1,215.6979   $1,215.69   $1,215.75   $1,215.70