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 $177.68   3.182%   $183.3338   $183.33   $183.35   $183.30  
  Purchase #2 $172.67   4.537%   $180.504   $180.50   $180.50   $180.50  
  Purchase #3 $154.92   11.159%   $172.2075   $172.21   $172.20   $172.20  
  Purchase #4 $236.84   13.610%   $269.0739   $269.07   $269.05   $269.10  
  Purchase #5 $194.82   12.337%   $218.8549   $218.85   $218.85   $218.90  
  Purchase #6 $121.79   5.291%   $128.2339   $128.23   $128.25   $128.20  
  Purchase #7 $62.50   7.586%   $67.2413   $67.24   $67.25   $67.20  
  7 purchase totals = $1,121.22       $1,219.4493   $1,219.43   $1,219.45   $1,219.40