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	$160.39	3.731%	$166.3742	$166.37	$166.35	$166.40
Purchase #2	$145.71	7.296%	$156.341	$156.34	$156.35	$156.30
Purchase #3	$86.27	11.727%	$96.3869	$96.39	$96.40	$96.40
Purchase #4	$136.36	6.680%	$145.4688	$145.47	$145.45	$145.50
Purchase #5	$86.82	7.565%	$93.3879	$93.39	$93.40	$93.40
Purchase #6	$61.71	9.119%	$67.3373	$67.34	$67.35	$67.30
Purchase #7	$132.48	10.820%	$146.8143	$146.81	$146.80	$146.80
7 purchase totals =	$809.74		$872.1104	$872.11	$872.10	$872.10