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 $28.71   11.788%   $32.0943   $32.09   $32.10   $32.10  
  Purchase #2 $245.37   13.420%   $278.2987   $278.30   $278.30   $278.30  
  Purchase #3 $250.60   13.692%   $284.9122   $284.91   $284.90   $284.90  
  Purchase #4 $238.66   12.353%   $268.1417   $268.14   $268.15   $268.10  
  Purchase #5 $230.52   9.293%   $251.9422   $251.94   $251.95   $251.90  
  Purchase #6 $185.50   7.822%   $200.0098   $200.01   $200.00   $200.00  
  Purchase #7 $168.49   8.627%   $183.0256   $183.03   $183.05   $183.00  
  7 purchase totals = $1,347.85       $1,498.4245   $1,498.42   $1,498.45   $1,498.30