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 $216.45   6.771%   $231.1058   $231.11   $231.10   $231.10  
  Purchase #2 $44.69   8.491%   $48.4846   $48.48   $48.50   $48.50  
  Purchase #3 $155.75   3.214%   $160.7558   $160.76   $160.75   $160.80  
  Purchase #4 $49.58   12.388%   $55.722   $55.72   $55.70   $55.70  
  Purchase #5 $246.34   12.203%   $276.4009   $276.40   $276.40   $276.40  
  Purchase #6 $217.53   6.280%   $231.1909   $231.19   $231.20   $231.20  
  Purchase #7 $25.81   13.162%   $29.2071   $29.21   $29.20   $29.20  
  7 purchase totals = $956.15       $1,032.8671   $1,032.87   $1,032.85   $1,032.90