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	$25.25	10.808%	$27.979	$27.98	$28.00	$28.00
Purchase #2	$17.45	7.360%	$18.7343	$18.73	$18.75	$18.70
Purchase #3	$114.63	13.734%	$130.3733	$130.37	$130.35	$130.40
Purchase #4	$244.32	13.506%	$277.3179	$277.32	$277.30	$277.30
Purchase #5	$35.77	3.322%	$36.9583	$36.96	$36.95	$37.00
Purchase #6	$90.93	10.311%	$100.3058	$100.31	$100.30	$100.30
Purchase #7	$144.56	9.427%	$158.1877	$158.19	$158.20	$158.20
7 purchase totals =	$672.91		$749.8563	$749.86	$749.85	$749.90