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 $41.57   11.619%   $46.4   $46.40   $46.40   $46.40  
  Purchase #2 $145.55   5.599%   $153.6993   $153.70   $153.70   $153.70  
  Purchase #3 $54.40   10.761%   $60.254   $60.25   $60.25   $60.30  
  Purchase #4 $200.82   10.344%   $221.5928   $221.59   $221.60   $221.60  
  Purchase #5 $97.40   8.255%   $105.4404   $105.44   $105.45   $105.40  
  Purchase #6 $68.56   12.606%   $77.2027   $77.20   $77.20   $77.20  
  Purchase #7 $175.40   5.719%   $185.4311   $185.43   $185.45   $185.40  
  7 purchase totals = $783.70       $850.0203   $850.01   $850.05   $850.00