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	$79.80	13.349%	$90.4525	$90.45	$90.45	$90.50
Purchase #2	$19.92	3.277%	$20.5728	$20.57	$20.55	$20.60
Purchase #3	$110.29	9.180%	$120.4146	$120.41	$120.40	$120.40
Purchase #4	$120.39	9.231%	$131.5032	$131.50	$131.50	$131.50
Purchase #5	$106.94	7.515%	$114.9765	$114.98	$115.00	$115.00
Purchase #6	$150.81	13.553%	$171.2493	$171.25	$171.25	$171.20
Purchase #7	$57.33	8.447%	$62.1727	$62.17	$62.15	$62.20
7 purchase totals =	$645.48		$711.3416	$711.33	$711.30	$711.40