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	$74.89	8.766%	$81.4549	$81.45	$81.45	$81.50
Purchase #2	$110.64	3.780%	$114.8222	$114.82	$114.80	$114.80
Purchase #3	$90.89	4.394%	$94.8837	$94.88	$94.90	$94.90
Purchase #4	$239.64	12.839%	$270.4074	$270.41	$270.40	$270.40
Purchase #5	$173.91	3.809%	$180.5342	$180.53	$180.55	$180.50
Purchase #6	$248.61	11.152%	$276.335	$276.34	$276.35	$276.30
Purchase #7	$152.68	9.558%	$167.2732	$167.27	$167.25	$167.30
7 purchase totals =	$1,091.26		$1,185.7106	$1,185.70	$1,185.70	$1,185.70