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	$180.33	4.575%	$188.5801	$188.58	$188.60	$188.60
Purchase #2	$82.27	9.299%	$89.9203	$89.92	$89.90	$89.90
Purchase #3	$36.32	12.784%	$40.9631	$40.96	$40.95	$41.00
Purchase #4	$63.46	3.797%	$65.8696	$65.87	$65.85	$65.90
Purchase #5	$107.81	7.452%	$115.844	$115.84	$115.85	$115.80
Purchase #6	$99.25	11.102%	$110.2687	$110.27	$110.25	$110.30
Purchase #7	$199.85	5.513%	$210.8677	$210.87	$210.85	$210.90
7 purchase totals =	$769.29		$822.3135	$822.31	$822.25	$822.40