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	$179.57	3.188%	$185.2947	$185.29	$185.30	$185.30
Purchase #2	$232.93	3.255%	$240.5119	$240.51	$240.50	$240.50
Purchase #3	$120.42	6.119%	$127.7885	$127.79	$127.80	$127.80
Purchase #4	$81.28	9.657%	$89.1292	$89.13	$89.15	$89.10
Purchase #5	$170.99	9.306%	$186.9023	$186.90	$186.90	$186.90
Purchase #6	$144.94	4.682%	$151.7261	$151.73	$151.75	$151.70
Purchase #7	$50.90	12.141%	$57.0798	$57.08	$57.10	$57.10
7 purchase totals =	$981.03		$1,038.4325	$1,038.43	$1,038.50	$1,038.40