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 $206.46   10.858%   $228.8774   $228.88   $228.90   $228.90  
  Purchase #2 $119.86   5.396%   $126.3276   $126.33   $126.35   $126.30  
  Purchase #3 $96.99   13.302%   $109.8916   $109.89   $109.90   $109.90  
  Purchase #4 $125.78   7.401%   $135.089   $135.09   $135.10   $135.10  
  Purchase #5 $78.43   10.670%   $86.7985   $86.80   $86.80   $86.80  
  Purchase #6 $61.82   10.215%   $68.1349   $68.13   $68.15   $68.10  
  Purchase #7 $246.46   6.357%   $262.1275   $262.13   $262.15   $262.10  
  7 purchase totals = $935.80       $1,017.2465   $1,017.25   $1,017.35   $1,017.20