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 $111.80   13.348%   $126.7231   $126.72   $126.70   $126.70  
  Purchase #2 $170.43   3.237%   $175.9468   $175.95   $175.95   $175.90  
  Purchase #3 $30.91   6.473%   $32.9108   $32.91   $32.90   $32.90  
  Purchase #4 $98.97   3.363%   $102.2984   $102.30   $102.30   $102.30  
  Purchase #5 $198.27   13.509%   $225.0543   $225.05   $225.05   $225.10  
  Purchase #6 $14.38   13.630%   $16.34   $16.34   $16.35   $16.30  
  Purchase #7 $84.91   8.797%   $92.3795   $92.38   $92.40   $92.40  
  7 purchase totals = $709.67       $771.6529   $771.65   $771.65   $771.60