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	$168.57	8.792%	$183.3907	$183.39	$183.40	$183.40
Purchase #2	$78.99	13.753%	$89.8535	$89.85	$89.85	$89.90
Purchase #3	$230.71	6.253%	$245.1363	$245.14	$245.15	$245.10
Purchase #4	$36.30	13.243%	$41.1072	$41.11	$41.10	$41.10
Purchase #5	$20.91	7.602%	$22.4996	$22.50	$22.50	$22.50
Purchase #6	$109.32	5.590%	$115.431	$115.43	$115.45	$115.40
Purchase #7	$114.84	7.423%	$123.3646	$123.36	$123.35	$123.40
7 purchase totals =	$759.64		$820.7829	$820.78	$820.80	$820.80