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	$231.29	12.780%	$260.8489	$260.85	$260.85	$260.80
Purchase #2	$131.82	10.285%	$145.3777	$145.38	$145.40	$145.40
Purchase #3	$98.46	11.753%	$110.032	$110.03	$110.05	$110.00
Purchase #4	$210.55	8.307%	$228.0404	$228.04	$228.05	$228.00
Purchase #5	$95.95	3.466%	$99.2756	$99.28	$99.30	$99.30
Purchase #6	$76.83	7.161%	$82.3318	$82.33	$82.35	$82.30
Purchase #7	$157.90	4.650%	$165.2424	$165.24	$165.25	$165.20
7 purchase totals =	$1,002.80		$1,091.1488	$1,091.15	$1,091.25	$1,091.00