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	$54.76	12.651%	$61.6877	$61.69	$61.70	$61.70
Purchase #2	$42.44	4.650%	$44.4135	$44.41	$44.40	$44.40
Purchase #3	$188.34	5.728%	$199.1281	$199.13	$199.15	$199.10
Purchase #4	$191.31	4.463%	$199.8482	$199.85	$199.85	$199.80
Purchase #5	$88.71	12.435%	$99.7411	$99.74	$99.75	$99.70
Purchase #6	$110.69	13.337%	$125.4527	$125.45	$125.45	$125.50
Purchase #7	$64.45	11.477%	$71.8469	$71.85	$71.85	$71.80
7 purchase totals =	$740.70		$802.1182	$802.12	$802.15	$802.00