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	$222.50	10.329%	$245.482	$245.48	$245.50	$245.50
Purchase #2	$237.52	6.810%	$253.6951	$253.70	$253.70	$253.70
Purchase #3	$69.56	6.135%	$73.8275	$73.83	$73.85	$73.80
Purchase #4	$114.80	13.768%	$130.6057	$130.61	$130.60	$130.60
Purchase #5	$237.74	5.385%	$250.5423	$250.54	$250.55	$250.50
Purchase #6	$86.44	4.487%	$90.3186	$90.32	$90.30	$90.30
Purchase #7	$84.57	5.298%	$89.0505	$89.05	$89.05	$89.10
7 purchase totals =	$1,053.13		$1,133.5217	$1,133.53	$1,133.55	$1,133.50