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 $62.57   6.380%   $66.562   $66.56   $66.55   $66.60  
  Purchase #2 $183.81   12.608%   $206.9848   $206.98   $207.00   $207.00  
  Purchase #3 $46.90   7.331%   $50.3382   $50.34   $50.35   $50.30  
  Purchase #4 $198.60   4.583%   $207.7018   $207.70   $207.70   $207.70  
  Purchase #5 $5.90   3.106%   $6.0833   $6.08   $6.10   $6.10  
  Purchase #6 $34.50   3.397%   $35.672   $35.67   $35.65   $35.70  
  Purchase #7 $30.53   13.842%   $34.756   $34.76   $34.75   $34.80  
  7 purchase totals = $562.81       $608.0981   $608.09   $608.10   $608.20