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	$199.63	11.158%	$221.9047	$221.90	$221.90	$221.90
Purchase #2	$148.56	4.740%	$155.6017	$155.60	$155.60	$155.60
Purchase #3	$66.26	7.368%	$71.142	$71.14	$71.15	$71.10
Purchase #4	$98.80	10.680%	$109.3518	$109.35	$109.35	$109.40
Purchase #5	$26.77	13.845%	$30.4763	$30.48	$30.50	$30.50
Purchase #6	$158.67	9.739%	$174.1229	$174.12	$174.10	$174.10
Purchase #7	$72.82	6.515%	$77.5642	$77.56	$77.55	$77.60
7 purchase totals =	$771.51		$840.1636	$840.15	$840.15	$840.20