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 $67.36   3.236%   $69.5398   $69.54   $69.55   $69.50  
  Purchase #2 $138.79   9.336%   $151.7474   $151.75   $151.75   $151.70  
  Purchase #3 $61.51   6.638%   $65.593   $65.59   $65.60   $65.60  
  Purchase #4 $248.83   13.477%   $282.3648   $282.36   $282.35   $282.40  
  Purchase #5 $157.36   9.581%   $172.4367   $172.44   $172.45   $172.40  
  Purchase #6 $58.58   7.872%   $63.1914   $63.19   $63.20   $63.20  
  Purchase #7 $15.50   7.685%   $16.6912   $16.69   $16.70   $16.70  
  7 purchase totals = $747.93       $821.5643   $821.56   $821.60   $821.50