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	$230.45	12.690%	$259.6941	$259.69	$259.70	$259.70
Purchase #2	$120.90	8.615%	$131.3155	$131.32	$131.30	$131.30
Purchase #3	$118.95	10.736%	$131.7205	$131.72	$131.70	$131.70
Purchase #4	$244.80	9.814%	$268.8247	$268.82	$268.80	$268.80
Purchase #5	$57.57	13.296%	$65.2245	$65.22	$65.20	$65.20
Purchase #6	$37.56	4.529%	$39.2611	$39.26	$39.25	$39.30
Purchase #7	$8.25	7.669%	$8.8827	$8.88	$8.90	$8.90
7 purchase totals =	$818.48		$904.9231	$904.91	$904.85	$904.90