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 $60.43   7.627%   $65.039   $65.04   $65.05   $65.00  
  Purchase #2 $198.56   11.313%   $221.0231   $221.02   $221.00   $221.00  
  Purchase #3 $16.77   5.215%   $17.6446   $17.64   $17.65   $17.60  
  Purchase #4 $247.40   7.715%   $266.4869   $266.49   $266.50   $266.50  
  Purchase #5 $188.25   11.728%   $210.328   $210.33   $210.35   $210.30  
  Purchase #6 $35.77   7.806%   $38.5622   $38.56   $38.55   $38.60  
  Purchase #7 $23.59   11.151%   $26.2205   $26.22   $26.20   $26.20  
  7 purchase totals = $770.77       $845.3043   $845.30   $845.30   $845.20