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 $167.79   3.505%   $173.671   $173.67   $173.65   $173.70  
  Purchase #2 $246.94   13.747%   $280.8868   $280.89   $280.90   $280.90  
  Purchase #3 $109.36   13.385%   $123.9978   $124.00   $124.00   $124.00  
  Purchase #4 $175.54   12.457%   $197.407   $197.41   $197.40   $197.40  
  Purchase #5 $32.77   5.537%   $34.5845   $34.58   $34.60   $34.60  
  Purchase #6 $33.72   3.186%   $34.7943   $34.79   $34.80   $34.80  
  Purchase #7 $107.77   7.690%   $116.0575   $116.06   $116.05   $116.10  
  7 purchase totals = $873.89       $961.3989   $961.40   $961.40   $961.50