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 $247.49   11.617%   $276.2409   $276.24   $276.25   $276.20  
  Purchase #2 $5.96   3.228%   $6.1524   $6.15   $6.15   $6.20  
  Purchase #3 $131.48   12.457%   $147.8585   $147.86   $147.85   $147.90  
  Purchase #4 $186.51   3.699%   $193.409   $193.41   $193.40   $193.40  
  Purchase #5 $230.96   7.751%   $248.8617   $248.86   $248.85   $248.90  
  Purchase #6 $135.98   3.760%   $141.0928   $141.09   $141.10   $141.10  
  Purchase #7 $162.65   12.574%   $183.1016   $183.10   $183.10   $183.10  
  7 purchase totals = $1,101.03       $1,196.7169   $1,196.71   $1,196.70   $1,196.80