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	$72.26	9.718%	$79.2822	$79.28	$79.30	$79.30
Purchase #2	$32.44	3.109%	$33.4486	$33.45	$33.45	$33.40
Purchase #3	$6.43	13.842%	$7.32	$7.32	$7.30	$7.30
Purchase #4	$190.34	11.110%	$211.4868	$211.49	$211.50	$211.50
Purchase #5	$187.46	11.575%	$209.1585	$209.16	$209.15	$209.20
Purchase #6	$62.36	12.642%	$70.2436	$70.24	$70.25	$70.20
Purchase #7	$89.74	12.206%	$100.6937	$100.69	$100.70	$100.70
7 purchase totals =	$641.03		$711.6334	$711.63	$711.65	$711.60