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 $92.90   13.296%   $105.252   $105.25   $105.25   $105.30  
  Purchase #2 $206.84   8.467%   $224.3531   $224.35   $224.35   $224.40  
  Purchase #3 $245.57   13.628%   $279.0363   $279.04   $279.05   $279.00  
  Purchase #4 $152.78   8.829%   $166.2689   $166.27   $166.25   $166.30  
  Purchase #5 $16.39   4.320%   $17.098   $17.10   $17.10   $17.10  
  Purchase #6 $53.94   12.552%   $60.7105   $60.71   $60.70   $60.70  
  Purchase #7 $200.64   8.812%   $218.3204   $218.32   $218.30   $218.30  
  7 purchase totals = $969.06       $1,071.0392   $1,071.04   $1,071.00   $1,071.10