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	$79.76	12.374%	$89.6295	$89.63	$89.65	$89.60
Purchase #2	$186.51	10.298%	$205.7168	$205.72	$205.70	$205.70
Purchase #3	$229.63	7.743%	$247.4103	$247.41	$247.40	$247.40
Purchase #4	$104.27	4.648%	$109.1165	$109.12	$109.10	$109.10
Purchase #5	$32.50	9.288%	$35.5186	$35.52	$35.50	$35.50
Purchase #6	$250.98	7.122%	$268.8548	$268.85	$268.85	$268.90
Purchase #7	$94.29	8.482%	$102.2877	$102.29	$102.30	$102.30
7 purchase totals =	$977.94		$1,058.5342	$1,058.54	$1,058.50	$1,058.50