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 $62.87   5.774%   $66.5001   $66.50   $66.50   $66.50  
  Purchase #2 $165.33   11.617%   $184.5364   $184.54   $184.55   $184.50  
  Purchase #3 $166.61   6.165%   $176.8815   $176.88   $176.90   $176.90  
  Purchase #4 $155.99   10.771%   $172.7917   $172.79   $172.80   $172.80  
  Purchase #5 $160.54   7.738%   $172.9626   $172.96   $172.95   $173.00  
  Purchase #6 $201.25   3.726%   $208.7486   $208.75   $208.75   $208.70  
  Purchase #7 $36.69   9.585%   $40.2067   $40.21   $40.20   $40.20  
  7 purchase totals = $949.28       $1,022.6276   $1,022.63   $1,022.65   $1,022.60