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	$121.98	4.130%	$127.0178	$127.02	$127.00	$127.00
Purchase #2	$45.53	8.250%	$49.2862	$49.29	$49.30	$49.30
Purchase #3	$25.27	12.572%	$28.4469	$28.45	$28.45	$28.40
Purchase #4	$179.80	10.173%	$198.0911	$198.09	$198.10	$198.10
Purchase #5	$250.78	5.284%	$264.0312	$264.03	$264.05	$264.00
Purchase #6	$76.72	5.390%	$80.8552	$80.86	$80.85	$80.90
Purchase #7	$250.29	9.860%	$274.9686	$274.97	$274.95	$275.00
7 purchase totals =	$950.37		$1,022.6970	$1,022.71	$1,022.70	$1,022.70