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 $226.49   13.692%   $257.501   $257.50   $257.50   $257.50  
  Purchase #2 $178.52   5.868%   $188.9956   $189.00   $189.00   $189.00  
  Purchase #3 $60.99   7.193%   $65.377   $65.38   $65.40   $65.40  
  Purchase #4 $121.91   5.354%   $128.4371   $128.44   $128.45   $128.40  
  Purchase #5 $39.83   6.508%   $42.4221   $42.42   $42.40   $42.40  
  Purchase #6 $104.51   9.459%   $114.3956   $114.40   $114.40   $114.40  
  Purchase #7 $205.83   3.864%   $213.7833   $213.78   $213.80   $213.80  
  7 purchase totals = $938.08       $1,010.9117   $1,010.92   $1,010.95   $1,010.90