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	$77.80	9.107%	$84.8852	$84.89	$84.90	$84.90
Purchase #2	$34.31	12.367%	$38.5531	$38.55	$38.55	$38.60
Purchase #3	$225.69	11.721%	$252.1431	$252.14	$252.15	$252.10
Purchase #4	$189.64	10.857%	$210.2292	$210.23	$210.25	$210.20
Purchase #5	$209.89	10.275%	$231.4562	$231.46	$231.45	$231.50
Purchase #6	$70.34	11.538%	$78.4558	$78.46	$78.45	$78.50
Purchase #7	$165.33	10.787%	$183.1641	$183.16	$183.15	$183.20
7 purchase totals =	$973.00		$1,078.8867	$1,078.89	$1,078.90	$1,079.00