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 $60.94   9.252%   $66.5782   $66.58   $66.60   $66.60  
  Purchase #2 $230.51   7.668%   $248.1855   $248.19   $248.20   $248.20  
  Purchase #3 $235.49   11.179%   $261.8154   $261.82   $261.80   $261.80  
  Purchase #4 $242.39   13.186%   $274.3515   $274.35   $274.35   $274.40  
  Purchase #5 $165.59   7.751%   $178.4249   $178.42   $178.40   $178.40  
  Purchase #6 $239.56   4.270%   $249.7892   $249.79   $249.80   $249.80  
  Purchase #7 $165.55   10.795%   $183.4211   $183.42   $183.40   $183.40  
  7 purchase totals = $1,340.03       $1,462.5658   $1,462.57   $1,462.55   $1,462.60