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 $129.74   11.723%   $144.9494   $144.95   $144.95   $144.90  
  Purchase #2 $208.57   4.220%   $217.3717   $217.37   $217.35   $217.40  
  Purchase #3 $226.55   11.233%   $251.9984   $252.00   $252.00   $252.00  
  Purchase #4 $197.45   6.120%   $209.5339   $209.53   $209.55   $209.50  
  Purchase #5 $63.63   5.409%   $67.0717   $67.07   $67.05   $67.10  
  Purchase #6 $225.25   13.868%   $256.4877   $256.49   $256.50   $256.50  
  Purchase #7 $64.77   3.615%   $67.1114   $67.11   $67.10   $67.10  
  7 purchase totals = $1,115.96       $1,214.5242   $1,214.52   $1,214.50   $1,214.50