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	$139.73	9.155%	$152.5223	$152.52	$152.50	$152.50
Purchase #2	$71.97	9.692%	$78.9453	$78.95	$78.95	$78.90
Purchase #3	$151.36	6.227%	$160.7852	$160.79	$160.80	$160.80
Purchase #4	$162.54	8.793%	$176.8321	$176.83	$176.85	$176.80
Purchase #5	$57.34	5.122%	$60.277	$60.28	$60.30	$60.30
Purchase #6	$101.25	8.294%	$109.6477	$109.65	$109.65	$109.60
Purchase #7	$170.45	5.232%	$179.3679	$179.37	$179.35	$179.40
7 purchase totals =	$854.64		$918.3775	$918.39	$918.40	$918.30