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 $166.26   10.485%   $183.6924   $183.69   $183.70   $183.70  
  Purchase #2 $82.84   13.117%   $93.7061   $93.71   $93.70   $93.70  
  Purchase #3 $129.81   4.156%   $135.2049   $135.20   $135.20   $135.20  
  Purchase #4 $35.94   4.659%   $37.6144   $37.61   $37.60   $37.60  
  Purchase #5 $45.62   11.503%   $50.8677   $50.87   $50.85   $50.90  
  Purchase #6 $70.32   5.627%   $74.2769   $74.28   $74.30   $74.30  
  Purchase #7 $26.26   4.142%   $27.3477   $27.35   $27.35   $27.30  
  7 purchase totals = $557.05       $602.7101   $602.71   $602.70   $602.70