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	$70.51	11.300%	$78.4776	$78.48	$78.50	$78.50
Purchase #2	$104.41	11.199%	$116.1029	$116.10	$116.10	$116.10
Purchase #3	$46.78	13.313%	$53.0078	$53.01	$53.00	$53.00
Purchase #4	$204.28	3.193%	$210.8027	$210.80	$210.80	$210.80
Purchase #5	$74.69	8.205%	$80.8183	$80.82	$80.80	$80.80
Purchase #6	$210.48	6.187%	$223.5024	$223.50	$223.50	$223.50
Purchase #7	$223.26	7.368%	$239.7098	$239.71	$239.70	$239.70
7 purchase totals =	$934.41		$1,002.4215	$1,002.42	$1,002.40	$1,002.40