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 $60.25   12.824%   $67.9765   $67.98   $68.00   $68.00  
  Purchase #2 $115.37   7.497%   $124.0193   $124.02   $124.00   $124.00  
  Purchase #3 $169.58   11.104%   $188.4102   $188.41   $188.40   $188.40  
  Purchase #4 $192.72   11.666%   $215.2027   $215.20   $215.20   $215.20  
  Purchase #5 $6.53   5.638%   $6.8982   $6.90   $6.90   $6.90  
  Purchase #6 $237.85   5.826%   $251.7071   $251.71   $251.70   $251.70  
  Purchase #7 $168.32   3.863%   $174.8222   $174.82   $174.80   $174.80  
  7 purchase totals = $950.62       $1,029.0362   $1,029.04   $1,029.00   $1,029.00