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 $58.65   3.276%   $60.5714   $60.57   $60.55   $60.60  
  Purchase #2 $176.42   12.795%   $198.9929   $198.99   $199.00   $199.00  
  Purchase #3 $155.99   6.277%   $165.7815   $165.78   $165.80   $165.80  
  Purchase #4 $246.46   8.366%   $267.0788   $267.08   $267.10   $267.10  
  Purchase #5 $191.62   7.545%   $206.0777   $206.08   $206.10   $206.10  
  Purchase #6 $46.69   3.743%   $48.4376   $48.44   $48.45   $48.40  
  Purchase #7 $21.79   7.426%   $23.4081   $23.41   $23.40   $23.40  
  7 purchase totals = $897.62       $970.3480   $970.35   $970.40   $970.40