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	$106.59	4.397%	$111.2768	$111.28	$111.30	$111.30
Purchase #2	$89.96	9.396%	$98.4126	$98.41	$98.40	$98.40
Purchase #3	$168.91	9.731%	$185.3466	$185.35	$185.35	$185.30
Purchase #4	$245.90	12.619%	$276.9301	$276.93	$276.95	$276.90
Purchase #5	$37.74	11.665%	$42.1424	$42.14	$42.15	$42.10
Purchase #6	$189.53	13.105%	$214.3679	$214.37	$214.35	$214.40
Purchase #7	$210.74	10.224%	$232.2861	$232.29	$232.30	$232.30
7 purchase totals =	$1,049.37		$1,160.7625	$1,160.77	$1,160.80	$1,160.70