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	$97.53	12.401%	$109.6247	$109.62	$109.60	$109.60
Purchase #2	$219.27	6.362%	$233.22	$233.22	$233.20	$233.20
Purchase #3	$30.98	7.799%	$33.3961	$33.40	$33.40	$33.40
Purchase #4	$142.42	7.843%	$153.59	$153.59	$153.60	$153.60
Purchase #5	$91.45	12.689%	$103.0541	$103.05	$103.05	$103.10
Purchase #6	$159.49	12.209%	$178.9621	$178.96	$178.95	$179.00
Purchase #7	$88.88	10.164%	$97.9138	$97.91	$97.90	$97.90
7 purchase totals =	$830.02		$909.7608	$909.75	$909.70	$909.80