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	$93.66	12.111%	$105.0032	$105.00	$105.00	$105.00
Purchase #2	$70.61	11.632%	$78.8234	$78.82	$78.80	$78.80
Purchase #3	$157.83	3.109%	$162.7369	$162.74	$162.75	$162.70
Purchase #4	$200.75	13.569%	$227.9898	$227.99	$228.00	$228.00
Purchase #5	$157.72	4.125%	$164.226	$164.23	$164.25	$164.20
Purchase #6	$6.50	12.594%	$7.3186	$7.32	$7.30	$7.30
Purchase #7	$239.55	7.359%	$257.1785	$257.18	$257.20	$257.20
7 purchase totals =	$926.62		$1,003.2764	$1,003.28	$1,003.30	$1,003.20