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 $50.42   6.792%   $53.8445   $53.84   $53.85   $53.80  
  Purchase #2 $33.25   6.640%   $35.4578   $35.46   $35.45   $35.50  
  Purchase #3 $208.69   10.714%   $231.049   $231.05   $231.05   $231.00  
  Purchase #4 $216.60   8.323%   $234.6276   $234.63   $234.65   $234.60  
  Purchase #5 $222.75   12.591%   $250.7965   $250.80   $250.80   $250.80  
  Purchase #6 $184.37   5.857%   $195.1686   $195.17   $195.15   $195.20  
  Purchase #7 $51.61   5.642%   $54.5218   $54.52   $54.50   $54.50  
  7 purchase totals = $967.69       $1,055.4658   $1,055.47   $1,055.45   $1,055.40