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	$38.87	4.158%	$40.4862	$40.49	$40.50	$40.50
Purchase #2	$142.39	6.562%	$151.7336	$151.73	$151.75	$151.70
Purchase #3	$102.57	6.303%	$109.035	$109.04	$109.05	$109.00
Purchase #4	$74.37	12.765%	$83.8633	$83.86	$83.85	$83.90
Purchase #5	$221.90	12.854%	$250.423	$250.42	$250.40	$250.40
Purchase #6	$103.74	5.170%	$109.1034	$109.10	$109.10	$109.10
Purchase #7	$105.86	5.316%	$111.4875	$111.49	$111.50	$111.50
7 purchase totals =	$789.70		$856.1320	$856.13	$856.15	$856.10