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 $119.78   7.536%   $128.8066   $128.81   $128.80   $128.80  
  Purchase #2 $63.46   3.774%   $65.855   $65.86   $65.85   $65.90  
  Purchase #3 $50.40   3.186%   $52.0057   $52.01   $52.00   $52.00  
  Purchase #4 $196.91   5.645%   $208.0256   $208.03   $208.05   $208.00  
  Purchase #5 $134.80   6.490%   $143.5485   $143.55   $143.55   $143.50  
  Purchase #6 $236.46   7.713%   $254.6982   $254.70   $254.70   $254.70  
  Purchase #7 $174.58   5.396%   $184.0003   $184.00   $184.00   $184.00  
  7 purchase totals = $976.39       $1,036.9399   $1,036.96   $1,036.95   $1,036.90