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	$171.97	11.358%	$191.5024	$191.50	$191.50	$191.50
Purchase #2	$113.33	3.851%	$117.6943	$117.69	$117.70	$117.70
Purchase #3	$115.86	6.452%	$123.3353	$123.34	$123.35	$123.30
Purchase #4	$73.71	9.262%	$80.537	$80.54	$80.55	$80.50
Purchase #5	$227.86	6.556%	$242.7985	$242.80	$242.80	$242.80
Purchase #6	$107.91	5.147%	$113.4641	$113.46	$113.45	$113.50
Purchase #7	$160.91	6.458%	$171.3016	$171.30	$171.30	$171.30
7 purchase totals =	$971.55		$1,040.6332	$1,040.63	$1,040.65	$1,040.60