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	$248.91	3.167%	$256.793	$256.79	$256.80	$256.80
Purchase #2	$175.97	8.229%	$190.4506	$190.45	$190.45	$190.50
Purchase #3	$223.61	8.293%	$242.154	$242.15	$242.15	$242.20
Purchase #4	$175.75	8.874%	$191.3461	$191.35	$191.35	$191.30
Purchase #5	$80.62	12.759%	$90.9063	$90.91	$90.90	$90.90
Purchase #6	$170.58	8.148%	$184.4789	$184.48	$184.50	$184.50
Purchase #7	$201.64	11.720%	$225.2722	$225.27	$225.25	$225.30
7 purchase totals =	$1,277.08		$1,381.4011	$1,381.40	$1,381.40	$1,381.50