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	$65.67	7.840%	$70.8185	$70.82	$70.80	$70.80
Purchase #2	$247.65	8.469%	$268.6235	$268.62	$268.60	$268.60
Purchase #3	$137.66	6.686%	$146.8639	$146.86	$146.85	$146.90
Purchase #4	$89.98	7.634%	$96.8491	$96.85	$96.85	$96.80
Purchase #5	$86.76	9.375%	$94.8938	$94.89	$94.90	$94.90
Purchase #6	$137.73	3.170%	$142.096	$142.10	$142.10	$142.10
Purchase #7	$231.37	11.640%	$258.3015	$258.30	$258.30	$258.30
7 purchase totals =	$996.82		$1,078.4463	$1,078.44	$1,078.40	$1,078.40