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 $7.69   10.507%   $8.498   $8.50   $8.50   $8.50  
  Purchase #2 $148.70   6.410%   $158.2317   $158.23   $158.25   $158.20  
  Purchase #3 $49.85   5.115%   $52.3998   $52.40   $52.40   $52.40  
  Purchase #4 $36.76   3.680%   $38.1128   $38.11   $38.10   $38.10  
  Purchase #5 $128.56   10.494%   $142.0511   $142.05   $142.05   $142.10  
  Purchase #6 $65.44   7.794%   $70.5404   $70.54   $70.55   $70.50  
  Purchase #7 $16.32   8.773%   $17.7518   $17.75   $17.75   $17.80  
  7 purchase totals = $453.32       $487.5856   $487.58   $487.60   $487.60