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 $56.58   6.660%   $60.3482   $60.35   $60.35   $60.30  
  Purchase #2 $180.94   8.203%   $195.7825   $195.78   $195.80   $195.80  
  Purchase #3 $107.40   4.777%   $112.5305   $112.53   $112.55   $112.50  
  Purchase #4 $173.41   9.144%   $189.2666   $189.27   $189.25   $189.30  
  Purchase #5 $196.25   9.584%   $215.0586   $215.06   $215.05   $215.10  
  Purchase #6 $208.56   10.318%   $230.0792   $230.08   $230.10   $230.10  
  Purchase #7 $195.35   3.413%   $202.0173   $202.02   $202.00   $202.00  
  7 purchase totals = $1,118.49       $1,205.0829   $1,205.09   $1,205.10   $1,205.10