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 $69.42   8.312%   $75.1902   $75.19   $75.20   $75.20  
  Purchase #2 $23.58   6.860%   $25.1976   $25.20   $25.20   $25.20  
  Purchase #3 $234.75   11.427%   $261.5749   $261.57   $261.55   $261.60  
  Purchase #4 $103.78   5.221%   $109.1984   $109.20   $109.20   $109.20  
  Purchase #5 $15.55   10.568%   $17.1933   $17.19   $17.20   $17.20  
  Purchase #6 $40.46   7.523%   $43.5038   $43.50   $43.50   $43.50  
  Purchase #7 $223.90   13.194%   $253.4414   $253.44   $253.45   $253.40  
  7 purchase totals = $711.44       $785.2996   $785.29   $785.30   $785.30