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	$16.86	13.289%	$19.1005	$19.10	$19.10	$19.10
Purchase #2	$43.97	4.352%	$45.8836	$45.88	$45.90	$45.90
Purchase #3	$93.99	8.427%	$101.9105	$101.91	$101.90	$101.90
Purchase #4	$174.94	12.844%	$197.4093	$197.41	$197.40	$197.40
Purchase #5	$67.58	6.381%	$71.8923	$71.89	$71.90	$71.90
Purchase #6	$118.25	4.412%	$123.4672	$123.47	$123.45	$123.50
Purchase #7	$105.30	5.460%	$111.0494	$111.05	$111.05	$111.00
7 purchase totals =	$620.89		$670.7128	$670.71	$670.70	$670.70