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 $248.57   10.826%   $275.4802   $275.48   $275.50   $275.50  
  Purchase #2 $95.83   3.491%   $99.1754   $99.18   $99.20   $99.20  
  Purchase #3 $23.82   3.790%   $24.7228   $24.72   $24.70   $24.70  
  Purchase #4 $151.48   9.443%   $165.7843   $165.78   $165.80   $165.80  
  Purchase #5 $111.47   3.379%   $115.2366   $115.24   $115.25   $115.20  
  Purchase #6 $135.52   13.321%   $153.5726   $153.57   $153.55   $153.60  
  Purchase #7 $124.39   9.686%   $136.4384   $136.44   $136.45   $136.40  
  7 purchase totals = $891.08       $970.4103   $970.41   $970.45   $970.40