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 $113.95   9.472%   $124.7433   $124.74   $124.75   $124.70  
  Purchase #2 $44.87   10.754%   $49.6953   $49.70   $49.70   $49.70  
  Purchase #3 $163.75   7.836%   $176.5815   $176.58   $176.60   $176.60  
  Purchase #4 $243.25   13.324%   $275.6606   $275.66   $275.65   $275.70  
  Purchase #5 $195.62   4.784%   $204.9785   $204.98   $205.00   $205.00  
  Purchase #6 $237.76   13.465%   $269.7744   $269.77   $269.75   $269.80  
  Purchase #7 $39.51   7.486%   $42.4677   $42.47   $42.45   $42.50  
  7 purchase totals = $1,038.71       $1,143.9013   $1,143.90   $1,143.90   $1,144.00