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	$49.89	11.719%	$55.7366	$55.74	$55.75	$55.70
Purchase #2	$136.28	11.790%	$152.3474	$152.35	$152.35	$152.30
Purchase #3	$248.35	9.253%	$271.3298	$271.33	$271.35	$271.30
Purchase #4	$165.56	7.565%	$178.0846	$178.08	$178.10	$178.10
Purchase #5	$56.48	9.484%	$61.8366	$61.84	$61.85	$61.80
Purchase #6	$47.29	11.768%	$52.8551	$52.86	$52.85	$52.90
Purchase #7	$63.76	5.170%	$67.0564	$67.06	$67.05	$67.10
7 purchase totals =	$767.61		$839.2465	$839.26	$839.30	$839.20