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 $86.99   10.508%   $96.1309   $96.13   $96.15   $96.10  
  Purchase #2 $201.91   9.260%   $220.6069   $220.61   $220.60   $220.60  
  Purchase #3 $90.89   4.606%   $95.0764   $95.08   $95.10   $95.10  
  Purchase #4 $226.85   9.458%   $248.3055   $248.31   $248.30   $248.30  
  Purchase #5 $236.29   5.224%   $248.6338   $248.63   $248.65   $248.60  
  Purchase #6 $223.99   10.292%   $247.0431   $247.04   $247.05   $247.00  
  Purchase #7 $99.56   3.864%   $103.407   $103.41   $103.40   $103.40  
  7 purchase totals = $1,166.48       $1,259.2036   $1,259.21   $1,259.25   $1,259.10