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	$99.91	13.315%	$113.213	$113.21	$113.20	$113.20
Purchase #2	$237.59	4.518%	$248.3243	$248.32	$248.30	$248.30
Purchase #3	$126.31	12.275%	$141.8146	$141.81	$141.80	$141.80
Purchase #4	$240.58	13.431%	$272.8923	$272.89	$272.90	$272.90
Purchase #5	$175.71	6.682%	$187.4509	$187.45	$187.45	$187.50
Purchase #6	$95.75	4.814%	$100.3594	$100.36	$100.35	$100.40
Purchase #7	$110.96	8.362%	$120.2385	$120.24	$120.25	$120.20
7 purchase totals =	$1,086.81		$1,184.2930	$1,184.28	$1,184.25	$1,184.30