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 $65.61   5.549%   $69.2507   $69.25   $69.25   $69.30  
  Purchase #2 $42.72   3.482%   $44.2075   $44.21   $44.20   $44.20  
  Purchase #3 $70.48   13.580%   $80.0512   $80.05   $80.05   $80.10  
  Purchase #4 $153.79   8.185%   $166.3777   $166.38   $166.40   $166.40  
  Purchase #5 $44.45   11.799%   $49.6947   $49.69   $49.70   $49.70  
  Purchase #6 $49.86   9.848%   $54.7702   $54.77   $54.75   $54.80  
  Purchase #7 $154.79   5.771%   $163.7229   $163.72   $163.70   $163.70  
  7 purchase totals = $581.70       $628.0749   $628.07   $628.05   $628.20