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	$70.92	11.281%	$78.9205	$78.92	$78.90	$78.90
Purchase #2	$64.76	11.607%	$72.2767	$72.28	$72.30	$72.30
Purchase #3	$174.99	6.240%	$185.9094	$185.91	$185.90	$185.90
Purchase #4	$190.94	10.352%	$210.7061	$210.71	$210.70	$210.70
Purchase #5	$163.69	10.102%	$180.226	$180.23	$180.25	$180.20
Purchase #6	$83.60	6.171%	$88.759	$88.76	$88.75	$88.80
Purchase #7	$174.56	9.245%	$190.6981	$190.70	$190.70	$190.70
7 purchase totals =	$923.46		$1,007.4958	$1,007.51	$1,007.50	$1,007.50