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 $208.94   8.165%   $226   $226.00   $226.00   $226.00  
  Purchase #2 $144.70   4.796%   $151.6398   $151.64   $151.65   $151.60  
  Purchase #3 $108.61   9.173%   $118.5728   $118.57   $118.55   $118.60  
  Purchase #4 $188.94   7.711%   $203.5092   $203.51   $203.50   $203.50  
  Purchase #5 $242.83   4.178%   $252.9754   $252.98   $253.00   $253.00  
  Purchase #6 $186.94   8.409%   $202.6598   $202.66   $202.65   $202.70  
  Purchase #7 $128.51   6.143%   $136.4044   $136.40   $136.40   $136.40  
  7 purchase totals = $1,209.47       $1,291.7614   $1,291.76   $1,291.75   $1,291.80