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	$34.41	3.769%	$35.7069	$35.71	$35.70	$35.70
Purchase #2	$189.89	5.227%	$199.8156	$199.82	$199.80	$199.80
Purchase #3	$52.27	9.519%	$57.2456	$57.25	$57.25	$57.20
Purchase #4	$99.76	13.805%	$113.5319	$113.53	$113.55	$113.50
Purchase #5	$211.54	13.603%	$240.3158	$240.32	$240.30	$240.30
Purchase #6	$93.41	3.753%	$96.9157	$96.92	$96.90	$96.90
Purchase #7	$111.56	4.366%	$116.4307	$116.43	$116.45	$116.40
7 purchase totals =	$792.84		$859.9622	$859.98	$859.95	$859.80