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 $5.43   6.187%   $5.766   $5.77   $5.75   $5.80  
  Purchase #2 $244.26   4.638%   $255.5888   $255.59   $255.60   $255.60  
  Purchase #3 $69.26   6.574%   $73.8132   $73.81   $73.80   $73.80  
  Purchase #4 $114.68   13.812%   $130.5196   $130.52   $130.50   $130.50  
  Purchase #5 $68.29   11.706%   $76.284   $76.28   $76.30   $76.30  
  Purchase #6 $172.26   11.665%   $192.3541   $192.35   $192.35   $192.40  
  Purchase #7 $127.26   10.369%   $140.4556   $140.46   $140.45   $140.50  
  7 purchase totals = $801.44       $874.7813   $874.78   $874.75   $874.90