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	$236.71	8.245%	$256.2267	$256.23	$256.25	$256.20
Purchase #2	$102.94	7.746%	$110.9137	$110.91	$110.90	$110.90
Purchase #3	$162.40	13.684%	$184.6228	$184.62	$184.60	$184.60
Purchase #4	$179.55	10.222%	$197.9036	$197.90	$197.90	$197.90
Purchase #5	$54.38	13.263%	$61.5924	$61.59	$61.60	$61.60
Purchase #6	$25.98	10.728%	$28.7671	$28.77	$28.75	$28.80
Purchase #7	$127.96	10.677%	$141.6223	$141.62	$141.60	$141.60
7 purchase totals =	$889.92		$981.6486	$981.64	$981.60	$981.60