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	$129.51	5.295%	$136.3676	$136.37	$136.35	$136.40
Purchase #2	$36.87	8.560%	$40.0261	$40.03	$40.05	$40.00
Purchase #3	$165.73	9.127%	$180.8562	$180.86	$180.85	$180.90
Purchase #4	$85.59	10.739%	$94.7815	$94.78	$94.80	$94.80
Purchase #5	$118.78	3.721%	$123.1998	$123.20	$123.20	$123.20
Purchase #6	$56.63	4.674%	$59.2769	$59.28	$59.30	$59.30
Purchase #7	$196.62	12.465%	$221.1287	$221.13	$221.15	$221.10
7 purchase totals =	$789.73		$855.6368	$855.65	$855.70	$855.70