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	$146.28	12.515%	$164.5869	$164.59	$164.60	$164.60
Purchase #2	$220.43	4.248%	$229.7939	$229.79	$229.80	$229.80
Purchase #3	$6.63	5.740%	$7.0106	$7.01	$7.00	$7.00
Purchase #4	$199.91	11.717%	$223.3335	$223.33	$223.35	$223.30
Purchase #5	$19.80	7.612%	$21.3072	$21.31	$21.30	$21.30
Purchase #6	$91.41	13.558%	$103.8034	$103.80	$103.80	$103.80
Purchase #7	$205.76	9.625%	$225.5644	$225.56	$225.55	$225.60
7 purchase totals =	$890.22		$975.3999	$975.39	$975.40	$975.40