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 $92.30   5.726%   $97.5851   $97.59   $97.60   $97.60  
  Purchase #2 $123.76   7.154%   $132.6138   $132.61   $132.60   $132.60  
  Purchase #3 $26.84   7.509%   $28.8554   $28.86   $28.85   $28.90  
  Purchase #4 $14.67   9.585%   $16.0761   $16.08   $16.10   $16.10  
  Purchase #5 $50.79   5.481%   $53.5738   $53.57   $53.55   $53.60  
  Purchase #6 $156.72   5.722%   $165.6875   $165.69   $165.70   $165.70  
  Purchase #7 $122.27   5.168%   $128.5889   $128.59   $128.60   $128.60  
  7 purchase totals = $587.35       $622.9806   $622.99   $623.00   $623.10