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 $216.78   11.396%   $241.4842   $241.48   $241.50   $241.50  
  Purchase #2 $207.25   12.423%   $232.9967   $233.00   $233.00   $233.00  
  Purchase #3 $91.55   4.133%   $95.3338   $95.33   $95.35   $95.30  
  Purchase #4 $48.51   10.811%   $53.7544   $53.75   $53.75   $53.80  
  Purchase #5 $139.55   6.255%   $148.2789   $148.28   $148.30   $148.30  
  Purchase #6 $89.90   5.772%   $95.089   $95.09   $95.10   $95.10  
  Purchase #7 $46.29   12.304%   $51.9855   $51.99   $52.00   $52.00  
  7 purchase totals = $839.83       $918.9225   $918.92   $919.00   $919.00