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 $249.52   10.466%   $275.6348   $275.63   $275.65   $275.60  
  Purchase #2 $136.98   5.497%   $144.5098   $144.51   $144.50   $144.50  
  Purchase #3 $27.29   4.495%   $28.5167   $28.52   $28.50   $28.50  
  Purchase #4 $140.74   10.405%   $155.384   $155.38   $155.40   $155.40  
  Purchase #5 $193.26   7.229%   $207.2308   $207.23   $207.25   $207.20  
  Purchase #6 $12.35   8.393%   $13.3865   $13.39   $13.40   $13.40  
  Purchase #7 $69.91   4.696%   $73.193   $73.19   $73.20   $73.20  
  7 purchase totals = $830.05       $897.8556   $897.85   $897.90   $897.80