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 $48.53   9.771%   $53.2719   $53.27   $53.25   $53.30  
  Purchase #2 $201.25   8.104%   $217.5593   $217.56   $217.55   $217.60  
  Purchase #3 $101.47   4.483%   $106.0189   $106.02   $106.00   $106.00  
  Purchase #4 $170.42   8.136%   $184.2854   $184.29   $184.30   $184.30  
  Purchase #5 $101.60   4.423%   $106.0938   $106.09   $106.10   $106.10  
  Purchase #6 $155.46   13.226%   $176.0211   $176.02   $176.00   $176.00  
  Purchase #7 $167.42   6.335%   $178.0261   $178.03   $178.05   $178.00  
  7 purchase totals = $946.15       $1,021.2765   $1,021.28   $1,021.25   $1,021.30