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	$81.35	11.796%	$90.946	$90.95	$90.95	$90.90
Purchase #2	$135.59	7.485%	$145.7389	$145.74	$145.75	$145.70
Purchase #3	$44.42	13.677%	$50.4953	$50.50	$50.50	$50.50
Purchase #4	$73.86	7.119%	$79.1181	$79.12	$79.10	$79.10
Purchase #5	$57.82	11.304%	$64.356	$64.36	$64.35	$64.40
Purchase #6	$38.38	10.211%	$42.299	$42.30	$42.30	$42.30
Purchase #7	$38.58	9.829%	$42.372	$42.37	$42.35	$42.40
7 purchase totals =	$470.00		$515.3253	$515.34	$515.30	$515.30