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	$52.60	5.626%	$55.5593	$55.56	$55.55	$55.60
Purchase #2	$224.75	13.208%	$254.435	$254.44	$254.45	$254.40
Purchase #3	$110.31	11.693%	$123.2085	$123.21	$123.20	$123.20
Purchase #4	$142.51	11.695%	$159.1765	$159.18	$159.20	$159.20
Purchase #5	$81.89	8.822%	$89.1143	$89.11	$89.10	$89.10
Purchase #6	$115.28	12.240%	$129.3903	$129.39	$129.40	$129.40
Purchase #7	$65.97	9.663%	$72.3447	$72.34	$72.35	$72.30
7 purchase totals =	$793.31		$883.2286	$883.23	$883.25	$883.20