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	$38.59	10.323%	$42.5736	$42.57	$42.55	$42.60
Purchase #2	$5.90	6.786%	$6.3004	$6.30	$6.30	$6.30
Purchase #3	$88.35	12.597%	$99.4794	$99.48	$99.50	$99.50
Purchase #4	$243.49	10.377%	$268.757	$268.76	$268.75	$268.80
Purchase #5	$228.75	4.837%	$239.8146	$239.81	$239.80	$239.80
Purchase #6	$11.90	4.614%	$12.4491	$12.45	$12.45	$12.40
Purchase #7	$79.94	11.848%	$89.4113	$89.41	$89.40	$89.40
7 purchase totals =	$696.92		$758.7854	$758.78	$758.75	$758.80