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	$18.77	11.179%	$20.8683	$20.87	$20.85	$20.90
Purchase #2	$196.58	13.296%	$222.7173	$222.72	$222.70	$222.70
Purchase #3	$227.63	11.644%	$254.1352	$254.14	$254.15	$254.10
Purchase #4	$185.43	11.114%	$206.0387	$206.04	$206.05	$206.00
Purchase #5	$111.29	10.645%	$123.1368	$123.14	$123.15	$123.10
Purchase #6	$106.85	4.396%	$111.5471	$111.55	$111.55	$111.50
Purchase #7	$79.45	5.165%	$83.5536	$83.55	$83.55	$83.60
7 purchase totals =	$926.00		$1,021.9970	$1,022.01	$1,022.00	$1,021.90