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 $68.61   3.856%   $71.2556   $71.26   $71.25   $71.30  
  Purchase #2 $214.71   13.435%   $243.5563   $243.56   $243.55   $243.60  
  Purchase #3 $58.83   9.264%   $64.28   $64.28   $64.30   $64.30  
  Purchase #4 $128.45   8.735%   $139.6701   $139.67   $139.65   $139.70  
  Purchase #5 $32.97   11.829%   $36.87   $36.87   $36.85   $36.90  
  Purchase #6 $138.97   4.463%   $145.1722   $145.17   $145.15   $145.20  
  Purchase #7 $12.79   4.853%   $13.4107   $13.41   $13.40   $13.40  
  7 purchase totals = $655.33       $714.2149   $714.22   $714.15   $714.40