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	$151.33	5.407%	$159.5124	$159.51	$159.50	$159.50
Purchase #2	$47.72	11.154%	$53.0427	$53.04	$53.05	$53.00
Purchase #3	$205.62	9.584%	$225.3266	$225.33	$225.35	$225.30
Purchase #4	$131.90	7.801%	$142.1895	$142.19	$142.20	$142.20
Purchase #5	$113.28	12.376%	$127.2995	$127.30	$127.30	$127.30
Purchase #6	$130.25	9.424%	$142.5248	$142.52	$142.50	$142.50
Purchase #7	$94.46	4.270%	$98.4934	$98.49	$98.50	$98.50
7 purchase totals =	$874.56		$948.3889	$948.38	$948.40	$948.30