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 $155.88   13.296%   $176.6058   $176.61   $176.60   $176.60  
  Purchase #2 $59.42   5.289%   $62.5627   $62.56   $62.55   $62.60  
  Purchase #3 $16.89   12.484%   $18.9985   $19.00   $19.00   $19.00  
  Purchase #4 $78.60   9.777%   $86.2847   $86.28   $86.30   $86.30  
  Purchase #5 $61.81   6.873%   $66.0582   $66.06   $66.05   $66.10  
  Purchase #6 $174.38   7.332%   $187.1655   $187.17   $187.15   $187.20  
  Purchase #7 $133.66   3.237%   $137.9866   $137.99   $138.00   $138.00  
  7 purchase totals = $680.64       $735.6620   $735.67   $735.65   $735.80