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	$179.47	4.499%	$187.5444	$187.54	$187.55	$187.50
Purchase #2	$36.56	11.573%	$40.7911	$40.79	$40.80	$40.80
Purchase #3	$20.28	6.735%	$21.6459	$21.65	$21.65	$21.60
Purchase #4	$30.81	12.648%	$34.7068	$34.71	$34.70	$34.70
Purchase #5	$63.31	9.399%	$69.2605	$69.26	$69.25	$69.30
Purchase #6	$25.43	13.515%	$28.8669	$28.87	$28.85	$28.90
Purchase #7	$68.46	5.254%	$72.0569	$72.06	$72.05	$72.10
7 purchase totals =	$424.32		$454.8725	$454.88	$454.85	$454.90