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 $100.37   4.775%   $105.1627   $105.16   $105.15   $105.20  
  Purchase #2 $145.48   12.379%   $163.489   $163.49   $163.50   $163.50  
  Purchase #3 $207.77   13.824%   $236.4921   $236.49   $236.50   $236.50  
  Purchase #4 $167.52   9.521%   $183.4696   $183.47   $183.45   $183.50  
  Purchase #5 $14.85   4.653%   $15.541   $15.54   $15.55   $15.50  
  Purchase #6 $119.78   5.667%   $126.5679   $126.57   $126.55   $126.60  
  Purchase #7 $107.34   6.843%   $114.6853   $114.69   $114.70   $114.70  
  7 purchase totals = $863.11       $945.4076   $945.41   $945.40   $945.50