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 $69.75   5.425%   $73.5339   $73.53   $73.55   $73.50  
  Purchase #2 $116.54   5.401%   $122.8343   $122.83   $122.85   $122.80  
  Purchase #3 $239.81   11.373%   $267.0836   $267.08   $267.10   $267.10  
  Purchase #4 $77.86   10.670%   $86.1677   $86.17   $86.15   $86.20  
  Purchase #5 $77.36   13.218%   $87.5854   $87.59   $87.60   $87.60  
  Purchase #6 $170.54   3.819%   $177.0529   $177.05   $177.05   $177.10  
  Purchase #7 $18.46   11.485%   $20.5801   $20.58   $20.60   $20.60  
  7 purchase totals = $770.32       $834.8379   $834.83   $834.90   $834.90