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	$91.92	12.849%	$103.7308	$103.73	$103.75	$103.70
Purchase #2	$171.78	13.140%	$194.3519	$194.35	$194.35	$194.40
Purchase #3	$105.66	3.471%	$109.3275	$109.33	$109.35	$109.30
Purchase #4	$76.87	3.774%	$79.7711	$79.77	$79.75	$79.80
Purchase #5	$39.83	13.192%	$45.0844	$45.08	$45.10	$45.10
Purchase #6	$141.69	13.580%	$160.9315	$160.93	$160.95	$160.90
Purchase #7	$84.83	4.127%	$88.3309	$88.33	$88.35	$88.30
7 purchase totals =	$712.58		$781.5281	$781.52	$781.60	$781.50