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 $85.60   7.827%   $92.2999   $92.30   $92.30   $92.30  
  Purchase #2 $174.76   9.159%   $190.7663   $190.77   $190.75   $190.80  
  Purchase #3 $176.95   10.287%   $195.1528   $195.15   $195.15   $195.20  
  Purchase #4 $221.35   13.361%   $250.9246   $250.92   $250.90   $250.90  
  Purchase #5 $181.37   6.777%   $193.6614   $193.66   $193.65   $193.70  
  Purchase #6 $165.53   6.759%   $176.7182   $176.72   $176.70   $176.70  
  Purchase #7 $115.98   10.219%   $127.832   $127.83   $127.85   $127.80  
  7 purchase totals = $1,121.54       $1,227.3552   $1,227.35   $1,227.30   $1,227.40