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 $52.95   9.523%   $57.9924   $57.99   $58.00   $58.00  
  Purchase #2 $70.93   7.198%   $76.0355   $76.04   $76.05   $76.00  
  Purchase #3 $242.48   13.555%   $275.3482   $275.35   $275.35   $275.30  
  Purchase #4 $112.40   12.789%   $126.7748   $126.77   $126.75   $126.80  
  Purchase #5 $244.33   9.750%   $268.1522   $268.15   $268.15   $268.20  
  Purchase #6 $60.67   5.239%   $63.8485   $63.85   $63.85   $63.80  
  Purchase #7 $200.96   8.544%   $218.13   $218.13   $218.15   $218.10  
  7 purchase totals = $984.72       $1,086.2816   $1,086.28   $1,086.30   $1,086.20