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	$134.81	3.474%	$139.4933	$139.49	$139.50	$139.50
Purchase #2	$98.98	5.839%	$104.7594	$104.76	$104.75	$104.80
Purchase #3	$119.75	10.131%	$131.8819	$131.88	$131.90	$131.90
Purchase #4	$94.31	6.203%	$100.16	$100.16	$100.15	$100.20
Purchase #5	$195.92	7.142%	$209.9126	$209.91	$209.90	$209.90
Purchase #6	$241.88	9.318%	$264.4184	$264.42	$264.40	$264.40
Purchase #7	$110.92	4.147%	$115.5199	$115.52	$115.50	$115.50
7 purchase totals =	$996.57		$1,066.1455	$1,066.14	$1,066.10	$1,066.20