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 $146.90   11.512%   $163.8111   $163.81   $163.80   $163.80  
  Purchase #2 $68.67   10.321%   $75.7574   $75.76   $75.75   $75.80  
  Purchase #3 $230.52   7.730%   $248.3392   $248.34   $248.35   $248.30  
  Purchase #4 $43.48   11.310%   $48.3976   $48.40   $48.40   $48.40  
  Purchase #5 $106.97   10.376%   $118.0692   $118.07   $118.05   $118.10  
  Purchase #6 $164.55   5.829%   $174.1416   $174.14   $174.15   $174.10  
  Purchase #7 $113.89   8.833%   $123.9499   $123.95   $123.95   $123.90  
  7 purchase totals = $874.98       $952.4660   $952.47   $952.45   $952.40