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 $41.44   4.512%   $43.3098   $43.31   $43.30   $43.30  
  Purchase #2 $97.90   10.367%   $108.0493   $108.05   $108.05   $108.00  
  Purchase #3 $179.84   7.106%   $192.6194   $192.62   $192.60   $192.60  
  Purchase #4 $180.56   5.418%   $190.3427   $190.34   $190.35   $190.30  
  Purchase #5 $222.87   7.562%   $239.7234   $239.72   $239.70   $239.70  
  Purchase #6 $55.53   13.453%   $63.0005   $63.00   $63.00   $63.00  
  Purchase #7 $118.88   10.861%   $131.7916   $131.79   $131.80   $131.80  
  7 purchase totals = $897.02       $968.8367   $968.83   $968.80   $968.70