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	$11.74	9.803%	$12.8909	$12.89	$12.90	$12.90
Purchase #2	$232.28	6.673%	$247.78	$247.78	$247.80	$247.80
Purchase #3	$59.38	6.645%	$63.3258	$63.33	$63.35	$63.30
Purchase #4	$99.77	11.812%	$111.5548	$111.55	$111.55	$111.60
Purchase #5	$99.64	3.625%	$103.252	$103.25	$103.25	$103.30
Purchase #6	$72.88	7.793%	$78.5595	$78.56	$78.55	$78.60
Purchase #7	$60.54	5.648%	$63.9593	$63.96	$63.95	$64.00
7 purchase totals =	$636.23		$681.3223	$681.32	$681.35	$681.50