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	$164.56	4.111%	$171.3251	$171.33	$171.35	$171.30
Purchase #2	$176.50	13.195%	$199.7892	$199.79	$199.80	$199.80
Purchase #3	$120.61	13.463%	$136.8477	$136.85	$136.85	$136.80
Purchase #4	$135.96	12.376%	$152.7864	$152.79	$152.80	$152.80
Purchase #5	$204.56	10.142%	$225.3065	$225.31	$225.30	$225.30
Purchase #6	$116.96	9.545%	$128.1238	$128.12	$128.10	$128.10
Purchase #7	$127.88	3.163%	$131.9248	$131.92	$131.90	$131.90
7 purchase totals =	$1,047.03		$1,146.1035	$1,146.11	$1,146.10	$1,146.00