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	$72.39	8.500%	$78.5432	$78.54	$78.55	$78.50
Purchase #2	$249.57	5.578%	$263.491	$263.49	$263.50	$263.50
Purchase #3	$129.44	13.461%	$146.8639	$146.86	$146.85	$146.90
Purchase #4	$6.75	12.534%	$7.596	$7.60	$7.60	$7.60
Purchase #5	$27.44	11.835%	$30.6875	$30.69	$30.70	$30.70
Purchase #6	$209.73	5.851%	$222.0013	$222.00	$222.00	$222.00
Purchase #7	$130.89	8.372%	$141.8481	$141.85	$141.85	$141.80
7 purchase totals =	$826.21		$891.0310	$891.03	$891.05	$891.00