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	$72.65	7.594%	$78.167	$78.17	$78.15	$78.20
Purchase #2	$225.86	4.734%	$236.5522	$236.55	$236.55	$236.60
Purchase #3	$7.58	6.680%	$8.0863	$8.09	$8.10	$8.10
Purchase #4	$157.93	6.547%	$168.2697	$168.27	$168.25	$168.30
Purchase #5	$170.66	5.535%	$180.106	$180.11	$180.10	$180.10
Purchase #6	$195.92	13.855%	$223.0647	$223.06	$223.05	$223.10
Purchase #7	$89.69	10.576%	$99.1756	$99.18	$99.20	$99.20
7 purchase totals =	$920.29		$993.4215	$993.43	$993.40	$993.60