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 $129.95   13.333%   $147.2762   $147.28   $147.30   $147.30  
  Purchase #2 $44.74   6.595%   $47.6906   $47.69   $47.70   $47.70  
  Purchase #3 $174.62   4.147%   $181.8615   $181.86   $181.85   $181.90  
  Purchase #4 $241.88   4.522%   $252.8178   $252.82   $252.80   $252.80  
  Purchase #5 $229.48   12.182%   $257.4353   $257.44   $257.45   $257.40  
  Purchase #6 $172.88   8.633%   $187.8047   $187.80   $187.80   $187.80  
  Purchase #7 $174.39   6.502%   $185.7288   $185.73   $185.75   $185.70  
  7 purchase totals = $1,167.94       $1,260.6149   $1,260.62   $1,260.65   $1,260.60