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	$99.29	13.300%	$112.4956	$112.50	$112.50	$112.50
Purchase #2	$52.97	12.512%	$59.5976	$59.60	$59.60	$59.60
Purchase #3	$223.37	12.503%	$251.298	$251.30	$251.30	$251.30
Purchase #4	$218.74	7.846%	$235.9023	$235.90	$235.90	$235.90
Purchase #5	$184.28	11.831%	$206.0822	$206.08	$206.10	$206.10
Purchase #6	$86.95	5.265%	$91.5279	$91.53	$91.55	$91.50
Purchase #7	$42.45	10.517%	$46.9145	$46.91	$46.90	$46.90
7 purchase totals =	$908.05		$1,003.8181	$1,003.82	$1,003.85	$1,003.80