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	$35.47	12.826%	$40.0194	$40.02	$40.00	$40.00
Purchase #2	$193.31	3.791%	$200.6384	$200.64	$200.65	$200.60
Purchase #3	$58.48	5.125%	$61.4771	$61.48	$61.50	$61.50
Purchase #4	$234.29	10.150%	$258.0704	$258.07	$258.05	$258.10
Purchase #5	$216.36	3.326%	$223.5561	$223.56	$223.55	$223.60
Purchase #6	$70.30	12.748%	$79.2618	$79.26	$79.25	$79.30
Purchase #7	$197.67	12.731%	$222.8354	$222.84	$222.85	$222.80
7 purchase totals =	$1,005.88		$1,085.8586	$1,085.87	$1,085.85	$1,085.90