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	$118.85	4.604%	$124.3219	$124.32	$124.30	$124.30
Purchase #2	$247.85	5.301%	$260.9885	$260.99	$261.00	$261.00
Purchase #3	$99.85	9.588%	$109.4236	$109.42	$109.40	$109.40
Purchase #4	$93.64	6.856%	$100.06	$100.06	$100.05	$100.10
Purchase #5	$200.50	3.694%	$207.9065	$207.91	$207.90	$207.90
Purchase #6	$128.32	6.776%	$137.015	$137.02	$137.00	$137.00
Purchase #7	$53.50	9.213%	$58.429	$58.43	$58.45	$58.40
7 purchase totals =	$942.51		$998.1445	$998.15	$998.10	$998.10