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	$39.83	7.581%	$42.8495	$42.85	$42.85	$42.80
Purchase #2	$77.90	4.840%	$81.6704	$81.67	$81.65	$81.70
Purchase #3	$59.27	10.182%	$65.3049	$65.30	$65.30	$65.30
Purchase #4	$237.50	5.419%	$250.3701	$250.37	$250.35	$250.40
Purchase #5	$110.93	4.378%	$115.7865	$115.79	$115.80	$115.80
Purchase #6	$99.79	3.324%	$103.107	$103.11	$103.10	$103.10
Purchase #7	$240.85	4.119%	$250.7706	$250.77	$250.75	$250.80
7 purchase totals =	$866.07		$909.8590	$909.86	$909.80	$909.90