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	$109.90	4.462%	$114.8037	$114.80	$114.80	$114.80
Purchase #2	$170.51	5.695%	$180.2205	$180.22	$180.20	$180.20
Purchase #3	$128.73	6.534%	$137.1412	$137.14	$137.15	$137.10
Purchase #4	$115.71	10.426%	$127.7739	$127.77	$127.75	$127.80
Purchase #5	$33.63	10.365%	$37.1157	$37.12	$37.10	$37.10
Purchase #6	$212.58	4.224%	$221.5594	$221.56	$221.55	$221.60
Purchase #7	$196.33	12.512%	$220.8948	$220.89	$220.90	$220.90
7 purchase totals =	$967.39		$1,039.5092	$1,039.50	$1,039.45	$1,039.50