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 $22.46   9.746%   $24.649   $24.65   $24.65   $24.60  
  Purchase #2 $40.95   11.208%   $45.5397   $45.54   $45.55   $45.50  
  Purchase #3 $57.71   12.348%   $64.836   $64.84   $64.85   $64.80  
  Purchase #4 $120.83   11.235%   $134.4053   $134.41   $134.40   $134.40  
  Purchase #5 $46.87   5.786%   $49.5819   $49.58   $49.60   $49.60  
  Purchase #6 $14.75   3.784%   $15.3081   $15.31   $15.30   $15.30  
  Purchase #7 $219.82   7.869%   $237.1176   $237.12   $237.10   $237.10  
  7 purchase totals = $523.39       $571.4376   $571.45   $571.45   $571.30