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 $159.52   10.323%   $175.9872   $175.99   $176.00   $176.00  
  Purchase #2 $129.52   9.501%   $141.8257   $141.83   $141.85   $141.80  
  Purchase #3 $124.26   5.102%   $130.5997   $130.60   $130.60   $130.60  
  Purchase #4 $225.81   4.687%   $236.3937   $236.39   $236.40   $236.40  
  Purchase #5 $36.82   12.444%   $41.4019   $41.40   $41.40   $41.40  
  Purchase #6 $145.60   13.276%   $164.9299   $164.93   $164.95   $164.90  
  Purchase #7 $148.99   6.238%   $158.284   $158.28   $158.30   $158.30  
  7 purchase totals = $970.52       $1,049.4221   $1,049.42   $1,049.50   $1,049.40