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	$8.88	4.630%	$9.2911	$9.29	$9.30	$9.30
Purchase #2	$38.61	9.526%	$42.288	$42.29	$42.30	$42.30
Purchase #3	$133.81	4.267%	$139.5197	$139.52	$139.50	$139.50
Purchase #4	$143.61	7.197%	$153.9456	$153.95	$153.95	$153.90
Purchase #5	$239.64	10.268%	$264.2462	$264.25	$264.25	$264.20
Purchase #6	$241.50	3.873%	$250.8533	$250.85	$250.85	$250.90
Purchase #7	$129.89	7.144%	$139.1693	$139.17	$139.15	$139.20
7 purchase totals =	$935.94		$999.3132	$999.32	$999.30	$999.30