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 $89.35   5.207%   $94.0025   $94.00   $94.00   $94.00  
  Purchase #2 $172.76   8.208%   $186.9401   $186.94   $186.95   $186.90  
  Purchase #3 $114.55   8.270%   $124.0233   $124.02   $124.00   $124.00  
  Purchase #4 $185.68   3.399%   $191.9913   $191.99   $192.00   $192.00  
  Purchase #5 $85.88   11.286%   $95.5724   $95.57   $95.55   $95.60  
  Purchase #6 $235.67   8.813%   $256.4396   $256.44   $256.45   $256.40  
  Purchase #7 $223.77   11.457%   $249.4073   $249.41   $249.40   $249.40  
  7 purchase totals = $1,107.66       $1,198.3765   $1,198.37   $1,198.35   $1,198.30