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 $52.37   10.411%   $57.8222   $57.82   $57.80   $57.80  
  Purchase #2 $185.62   9.299%   $202.8808   $202.88   $202.90   $202.90  
  Purchase #3 $16.40   13.241%   $18.5715   $18.57   $18.55   $18.60  
  Purchase #4 $147.79   7.659%   $159.1092   $159.11   $159.10   $159.10  
  Purchase #5 $72.32   13.577%   $82.1389   $82.14   $82.15   $82.10  
  Purchase #6 $207.96   11.573%   $232.0272   $232.03   $232.05   $232.00  
  Purchase #7 $147.61   9.856%   $162.1584   $162.16   $162.15   $162.20  
  7 purchase totals = $830.07       $914.7082   $914.71   $914.70   $914.70