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 $217.47   11.181%   $241.7853   $241.79   $241.80   $241.80  
  Purchase #2 $166.72   5.623%   $176.0947   $176.09   $176.10   $176.10  
  Purchase #3 $49.81   12.771%   $56.1712   $56.17   $56.15   $56.20  
  Purchase #4 $207.49   13.712%   $235.941   $235.94   $235.95   $235.90  
  Purchase #5 $150.58   5.227%   $158.4508   $158.45   $158.45   $158.50  
  Purchase #6 $163.31   13.381%   $185.1625   $185.16   $185.15   $185.20  
  Purchase #7 $9.73   3.847%   $10.1043   $10.10   $10.10   $10.10  
  7 purchase totals = $965.11       $1,063.7098   $1,063.70   $1,063.70   $1,063.80