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 $246.53   9.444%   $269.8123   $269.81   $269.80   $269.80  
  Purchase #2 $156.32   6.204%   $166.0181   $166.02   $166.00   $166.00  
  Purchase #3 $126.66   7.705%   $136.4192   $136.42   $136.40   $136.40  
  Purchase #4 $250.96   10.228%   $276.6282   $276.63   $276.65   $276.60  
  Purchase #5 $228.26   9.857%   $250.7596   $250.76   $250.75   $250.80  
  Purchase #6 $217.30   3.635%   $225.1989   $225.20   $225.20   $225.20  
  Purchase #7 $206.90   7.777%   $222.9906   $222.99   $223.00   $223.00  
  7 purchase totals = $1,432.93       $1,547.8269   $1,547.83   $1,547.80   $1,547.80