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 $62.64   12.136%   $70.242   $70.24   $70.25   $70.20  
  Purchase #2 $31.73   3.663%   $32.8923   $32.89   $32.90   $32.90  
  Purchase #3 $163.37   8.334%   $176.9853   $176.99   $177.00   $177.00  
  Purchase #4 $168.34   8.165%   $182.085   $182.09   $182.10   $182.10  
  Purchase #5 $91.40   13.764%   $103.9803   $103.98   $104.00   $104.00  
  Purchase #6 $213.34   8.765%   $232.0393   $232.04   $232.05   $232.00  
  Purchase #7 $233.28   6.330%   $248.0466   $248.05   $248.05   $248.00  
  7 purchase totals = $964.10       $1,046.2708   $1,046.28   $1,046.35   $1,046.20