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	$83.92	6.813%	$89.6375	$89.64	$89.65	$89.60
Purchase #2	$50.83	12.587%	$57.228	$57.23	$57.25	$57.20
Purchase #3	$154.31	11.608%	$172.2223	$172.22	$172.20	$172.20
Purchase #4	$235.74	10.683%	$260.9241	$260.92	$260.90	$260.90
Purchase #5	$248.48	10.816%	$275.3556	$275.36	$275.35	$275.40
Purchase #6	$43.85	9.146%	$47.8605	$47.86	$47.85	$47.90
Purchase #7	$123.60	6.459%	$131.5833	$131.58	$131.60	$131.60
7 purchase totals =	$940.73		$1,034.8113	$1,034.81	$1,034.80	$1,034.80