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 $140.69   9.466%   $154.0077   $154.01   $154.00   $154.00  
  Purchase #2 $231.81   5.518%   $244.6013   $244.60   $244.60   $244.60  
  Purchase #3 $178.28   5.111%   $187.3919   $187.39   $187.40   $187.40  
  Purchase #4 $218.86   7.638%   $235.5765   $235.58   $235.60   $235.60  
  Purchase #5 $60.29   10.827%   $66.8176   $66.82   $66.80   $66.80  
  Purchase #6 $131.84   12.301%   $148.0576   $148.06   $148.05   $148.10  
  Purchase #7 $111.61   13.368%   $126.53   $126.53   $126.55   $126.50  
  7 purchase totals = $1,073.38       $1,162.9826   $1,162.99   $1,163.00   $1,163.00