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 $228.67   5.543%   $241.3452   $241.35   $241.35   $241.30  
  Purchase #2 $122.59   3.441%   $126.8083   $126.81   $126.80   $126.80  
  Purchase #3 $221.28   7.686%   $238.2876   $238.29   $238.30   $238.30  
  Purchase #4 $157.49   6.356%   $167.5001   $167.50   $167.50   $167.50  
  Purchase #5 $179.61   10.358%   $198.214   $198.21   $198.20   $198.20  
  Purchase #6 $108.97   11.380%   $121.3708   $121.37   $121.35   $121.40  
  Purchase #7 $127.99   10.640%   $141.6081   $141.61   $141.60   $141.60  
  7 purchase totals = $1,146.60       $1,235.1341   $1,235.14   $1,235.10   $1,235.10