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 $30.96   11.633%   $34.5616   $34.56   $34.55   $34.60  
  Purchase #2 $47.82   6.246%   $50.8068   $50.81   $50.80   $50.80  
  Purchase #3 $245.42   5.372%   $258.604   $258.60   $258.60   $258.60  
  Purchase #4 $80.58   6.691%   $85.9716   $85.97   $85.95   $86.00  
  Purchase #5 $224.36   12.301%   $251.9585   $251.96   $251.95   $252.00  
  Purchase #6 $118.76   6.446%   $126.4153   $126.42   $126.40   $126.40  
  Purchase #7 $127.77   13.168%   $144.5948   $144.59   $144.60   $144.60  
  7 purchase totals = $875.67       $952.9126   $952.91   $952.85   $953.00