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 $248.86   5.573%   $262.729   $262.73   $262.75   $262.70  
  Purchase #2 $239.86   4.229%   $250.0037   $250.00   $250.00   $250.00  
  Purchase #3 $164.85   9.319%   $180.2124   $180.21   $180.20   $180.20  
  Purchase #4 $219.46   13.268%   $248.578   $248.58   $248.60   $248.60  
  Purchase #5 $178.83   8.513%   $194.0538   $194.05   $194.05   $194.10  
  Purchase #6 $39.46   7.721%   $42.5067   $42.51   $42.50   $42.50  
  Purchase #7 $180.44   5.598%   $190.541   $190.54   $190.55   $190.50  
  7 purchase totals = $1,271.76       $1,368.6246   $1,368.62   $1,368.65   $1,368.60