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	$32.78	6.323%	$34.8527	$34.85	$34.85	$34.90
Purchase #2	$75.46	7.517%	$81.1323	$81.13	$81.15	$81.10
Purchase #3	$142.76	6.759%	$152.4091	$152.41	$152.40	$152.40
Purchase #4	$110.67	9.222%	$120.876	$120.88	$120.90	$120.90
Purchase #5	$136.45	10.870%	$151.2821	$151.28	$151.30	$151.30
Purchase #6	$180.90	8.760%	$196.7468	$196.75	$196.75	$196.70
Purchase #7	$39.42	7.686%	$42.4498	$42.45	$42.45	$42.40
7 purchase totals =	$718.44		$779.7488	$779.75	$779.80	$779.70