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	$227.96	5.639%	$240.8147	$240.81	$240.80	$240.80
Purchase #2	$215.75	11.594%	$240.7641	$240.76	$240.75	$240.80
Purchase #3	$62.95	13.134%	$71.2179	$71.22	$71.20	$71.20
Purchase #4	$56.85	8.428%	$61.6413	$61.64	$61.65	$61.60
Purchase #5	$128.73	10.514%	$142.2647	$142.26	$142.25	$142.30
Purchase #6	$134.34	6.526%	$143.107	$143.11	$143.10	$143.10
Purchase #7	$17.56	3.152%	$18.1135	$18.11	$18.10	$18.10
7 purchase totals =	$844.14		$917.9232	$917.91	$917.85	$917.90