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	$142.55	3.413%	$147.4152	$147.42	$147.40	$147.40
Purchase #2	$95.63	11.187%	$106.3281	$106.33	$106.35	$106.30
Purchase #3	$248.34	13.171%	$281.0489	$281.05	$281.05	$281.00
Purchase #4	$139.75	4.180%	$145.5916	$145.59	$145.60	$145.60
Purchase #5	$56.56	9.657%	$62.022	$62.02	$62.00	$62.00
Purchase #6	$110.48	7.253%	$118.4931	$118.49	$118.50	$118.50
Purchase #7	$104.64	4.796%	$109.6585	$109.66	$109.65	$109.70
7 purchase totals =	$897.95		$970.5574	$970.56	$970.55	$970.50