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 $222.80   8.177%   $241.0184   $241.02   $241.00   $241.00  
  Purchase #2 $124.59   6.689%   $132.9238   $132.92   $132.90   $132.90  
  Purchase #3 $151.45   13.348%   $171.6655   $171.67   $171.65   $171.70  
  Purchase #4 $51.86   4.271%   $54.0749   $54.07   $54.05   $54.10  
  Purchase #5 $28.46   11.177%   $31.641   $31.64   $31.65   $31.60  
  Purchase #6 $232.88   8.622%   $252.9589   $252.96   $252.95   $253.00  
  Purchase #7 $150.39   13.739%   $171.0521   $171.05   $171.05   $171.10  
  7 purchase totals = $962.43       $1,055.3346   $1,055.33   $1,055.25   $1,055.40