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 $141.59   12.407%   $159.1571   $159.16   $159.15   $159.20  
  Purchase #2 $176.72   4.866%   $185.3192   $185.32   $185.30   $185.30  
  Purchase #3 $44.52   4.616%   $46.575   $46.58   $46.60   $46.60  
  Purchase #4 $148.89   10.385%   $164.3522   $164.35   $164.35   $164.40  
  Purchase #5 $113.64   7.537%   $122.205   $122.21   $122.20   $122.20  
  Purchase #6 $14.46   12.368%   $16.2484   $16.25   $16.25   $16.20  
  Purchase #7 $48.42   11.117%   $53.8029   $53.80   $53.80   $53.80  
  7 purchase totals = $688.24       $747.6598   $747.67   $747.65   $747.70