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 $85.90   8.868%   $93.5176   $93.52   $93.50   $93.50  
  Purchase #2 $88.29   4.539%   $92.2975   $92.30   $92.30   $92.30  
  Purchase #3 $104.95   13.327%   $118.9367   $118.94   $118.95   $118.90  
  Purchase #4 $211.68   5.643%   $223.6251   $223.63   $223.65   $223.60  
  Purchase #5 $174.85   3.458%   $180.8963   $180.90   $180.90   $180.90  
  Purchase #6 $238.99   8.489%   $259.2779   $259.28   $259.30   $259.30  
  Purchase #7 $14.61   7.830%   $15.754   $15.75   $15.75   $15.80  
  7 purchase totals = $919.27       $984.3051   $984.32   $984.35   $984.30