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	$91.49	13.317%	$103.6737	$103.67	$103.65	$103.70
Purchase #2	$34.47	4.207%	$35.9202	$35.92	$35.90	$35.90
Purchase #3	$235.69	13.473%	$267.4445	$267.44	$267.45	$267.40
Purchase #4	$216.46	3.341%	$223.6919	$223.69	$223.70	$223.70
Purchase #5	$79.66	11.842%	$89.0933	$89.09	$89.10	$89.10
Purchase #6	$181.85	12.270%	$204.163	$204.16	$204.15	$204.20
Purchase #7	$102.65	8.504%	$111.3794	$111.38	$111.40	$111.40
7 purchase totals =	$942.27		$1,035.3660	$1,035.35	$1,035.35	$1,035.40