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 $83.83   9.658%   $91.9263   $91.93   $91.95   $91.90  
  Purchase #2 $96.89   11.345%   $107.8822   $107.88   $107.90   $107.90  
  Purchase #3 $50.88   13.194%   $57.5931   $57.59   $57.60   $57.60  
  Purchase #4 $163.78   6.246%   $174.0097   $174.01   $174.00   $174.00  
  Purchase #5 $235.41   10.433%   $259.9703   $259.97   $259.95   $260.00  
  Purchase #6 $226.42   13.147%   $256.1874   $256.19   $256.20   $256.20  
  Purchase #7 $214.48   10.224%   $236.4084   $236.41   $236.40   $236.40  
  7 purchase totals = $1,071.69       $1,183.9774   $1,183.98   $1,184.00   $1,184.00