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 $83.93   11.524%   $93.6021   $93.60   $93.60   $93.60  
  Purchase #2 $155.99   3.872%   $162.0299   $162.03   $162.05   $162.00  
  Purchase #3 $134.56   3.512%   $139.2857   $139.29   $139.30   $139.30  
  Purchase #4 $25.92   6.229%   $27.5346   $27.53   $27.55   $27.50  
  Purchase #5 $177.77   3.862%   $184.6355   $184.64   $184.65   $184.60  
  Purchase #6 $62.49   5.862%   $66.1532   $66.15   $66.15   $66.20  
  Purchase #7 $117.26   5.215%   $123.3751   $123.38   $123.40   $123.40  
  7 purchase totals = $757.92       $796.6161   $796.62   $796.70   $796.60