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 $57.98   12.628%   $65.3017   $65.30   $65.30   $65.30  
  Purchase #2 $152.85   13.411%   $173.3487   $173.35   $173.35   $173.30  
  Purchase #3 $129.65   4.430%   $135.3935   $135.39   $135.40   $135.40  
  Purchase #4 $148.57   3.750%   $154.1414   $154.14   $154.15   $154.10  
  Purchase #5 $185.86   12.204%   $208.5424   $208.54   $208.55   $208.50  
  Purchase #6 $168.69   9.466%   $184.6582   $184.66   $184.65   $184.70  
  Purchase #7 $108.61   5.176%   $114.2317   $114.23   $114.25   $114.20  
  7 purchase totals = $952.21       $1,035.6176   $1,035.61   $1,035.65   $1,035.50