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 $238.94   8.394%   $258.9966   $259.00   $259.00   $259.00  
  Purchase #2 $171.43   8.487%   $185.9793   $185.98   $186.00   $186.00  
  Purchase #3 $120.94   7.312%   $129.7831   $129.78   $129.80   $129.80  
  Purchase #4 $48.91   9.578%   $53.5946   $53.59   $53.60   $53.60  
  Purchase #5 $34.79   3.443%   $35.9878   $35.99   $36.00   $36.00  
  Purchase #6 $246.78   4.397%   $257.6309   $257.63   $257.65   $257.60  
  Purchase #7 $110.64   11.596%   $123.4698   $123.47   $123.45   $123.50  
  7 purchase totals = $972.43       $1,045.4421   $1,045.44   $1,045.50   $1,045.50