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	$48.55	13.503%	$55.1057	$55.11	$55.10	$55.10
Purchase #2	$25.66	7.558%	$27.5994	$27.60	$27.60	$27.60
Purchase #3	$211.79	12.640%	$238.5603	$238.56	$238.55	$238.60
Purchase #4	$178.78	8.744%	$194.4125	$194.41	$194.40	$194.40
Purchase #5	$137.96	10.732%	$152.7659	$152.77	$152.75	$152.80
Purchase #6	$224.35	10.822%	$248.6292	$248.63	$248.65	$248.60
Purchase #7	$53.94	13.427%	$61.1825	$61.18	$61.20	$61.20
7 purchase totals =	$881.03		$978.2555	$978.26	$978.25	$978.30