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 $241.51   6.328%   $256.7928   $256.79   $256.80   $256.80  
  Purchase #2 $126.44   7.509%   $135.9344   $135.93   $135.95   $135.90  
  Purchase #3 $95.50   3.265%   $98.6181   $98.62   $98.60   $98.60  
  Purchase #4 $61.52   7.690%   $66.2509   $66.25   $66.25   $66.30  
  Purchase #5 $10.62   3.129%   $10.9523   $10.95   $10.95   $11.00  
  Purchase #6 $94.42   6.285%   $100.3543   $100.35   $100.35   $100.40  
  Purchase #7 $173.99   10.750%   $192.6939   $192.69   $192.70   $192.70  
  7 purchase totals = $804.00       $861.5967   $861.58   $861.60   $861.70