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	$176.96	6.729%	$188.8676	$188.87	$188.85	$188.90
Purchase #2	$105.51	5.263%	$111.063	$111.06	$111.05	$111.10
Purchase #3	$225.85	3.496%	$233.7457	$233.75	$233.75	$233.70
Purchase #4	$83.78	7.712%	$90.2411	$90.24	$90.25	$90.20
Purchase #5	$86.56	11.310%	$96.3499	$96.35	$96.35	$96.30
Purchase #6	$73.70	11.333%	$82.0524	$82.05	$82.05	$82.10
Purchase #7	$7.30	6.677%	$7.7874	$7.79	$7.80	$7.80
7 purchase totals =	$759.66		$810.1071	$810.11	$810.10	$810.10