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 $58.99   6.829%   $63.0184   $63.02   $63.00   $63.00  
  Purchase #2 $233.91   12.821%   $263.8996   $263.90   $263.90   $263.90  
  Purchase #3 $21.48   11.719%   $23.9972   $24.00   $24.00   $24.00  
  Purchase #4 $151.73   13.231%   $171.8054   $171.81   $171.80   $171.80  
  Purchase #5 $174.82   9.212%   $190.9244   $190.92   $190.90   $190.90  
  Purchase #6 $236.36   12.480%   $265.8577   $265.86   $265.85   $265.90  
  Purchase #7 $89.76   8.346%   $97.2514   $97.25   $97.25   $97.30  
  7 purchase totals = $967.05       $1,076.7541   $1,076.76   $1,076.70   $1,076.80