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 $52.43   10.194%   $57.7747   $57.77   $57.75   $57.80  
  Purchase #2 $133.90   11.531%   $149.34   $149.34   $149.35   $149.30  
  Purchase #3 $147.66   11.739%   $164.9938   $164.99   $165.00   $165.00  
  Purchase #4 $246.55   10.831%   $273.2538   $273.25   $273.25   $273.30  
  Purchase #5 $177.63   12.726%   $200.2352   $200.24   $200.25   $200.20  
  Purchase #6 $78.54   8.852%   $85.4924   $85.49   $85.50   $85.50  
  Purchase #7 $159.34   8.391%   $172.7102   $172.71   $172.70   $172.70  
  7 purchase totals = $996.05       $1,103.8001   $1,103.79   $1,103.80   $1,103.80