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	$48.74	11.299%	$54.2471	$54.25	$54.25	$54.20
Purchase #2	$70.43	4.358%	$73.4993	$73.50	$73.50	$73.50
Purchase #3	$32.45	8.300%	$35.1434	$35.14	$35.15	$35.10
Purchase #4	$102.83	6.139%	$109.1427	$109.14	$109.15	$109.10
Purchase #5	$195.46	11.684%	$218.2975	$218.30	$218.30	$218.30
Purchase #6	$139.40	8.226%	$150.867	$150.87	$150.85	$150.90
Purchase #7	$38.46	9.585%	$42.1464	$42.15	$42.15	$42.10
7 purchase totals =	$627.77		$683.3434	$683.35	$683.35	$683.20