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	$110.32	4.372%	$115.1432	$115.14	$115.15	$115.10
Purchase #2	$223.32	13.640%	$253.7808	$253.78	$253.80	$253.80
Purchase #3	$198.97	12.322%	$223.4871	$223.49	$223.50	$223.50
Purchase #4	$101.91	12.292%	$114.4368	$114.44	$114.45	$114.40
Purchase #5	$165.66	7.610%	$178.2667	$178.27	$178.25	$178.30
Purchase #6	$78.72	13.841%	$89.6156	$89.62	$89.60	$89.60
Purchase #7	$42.59	6.223%	$45.2404	$45.24	$45.25	$45.20
7 purchase totals =	$921.49		$1,019.9706	$1,019.98	$1,020.00	$1,019.90