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	$160.64	11.624%	$179.3128	$179.31	$179.30	$179.30
Purchase #2	$248.35	13.359%	$281.5271	$281.53	$281.55	$281.50
Purchase #3	$87.91	13.223%	$99.5343	$99.53	$99.55	$99.50
Purchase #4	$242.92	10.521%	$268.4776	$268.48	$268.50	$268.50
Purchase #5	$242.97	11.268%	$270.3479	$270.35	$270.35	$270.30
Purchase #6	$59.45	8.827%	$64.6977	$64.70	$64.70	$64.70
Purchase #7	$50.29	8.292%	$54.46	$54.46	$54.45	$54.50
7 purchase totals =	$1,092.53		$1,218.3574	$1,218.36	$1,218.40	$1,218.30