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	$157.50	7.136%	$168.7392	$168.74	$168.75	$168.70
Purchase #2	$109.58	13.402%	$124.2659	$124.27	$124.25	$124.30
Purchase #3	$146.59	7.783%	$157.9991	$158.00	$158.00	$158.00
Purchase #4	$232.72	3.263%	$240.3137	$240.31	$240.30	$240.30
Purchase #5	$127.83	11.587%	$142.6417	$142.64	$142.65	$142.60
Purchase #6	$189.39	9.706%	$207.7722	$207.77	$207.75	$207.80
Purchase #7	$96.42	13.171%	$109.1195	$109.12	$109.10	$109.10
7 purchase totals =	$1,060.03		$1,150.8513	$1,150.85	$1,150.80	$1,150.80