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	$77.30	7.206%	$82.8702	$82.87	$82.85	$82.90
Purchase #2	$211.43	13.583%	$240.1485	$240.15	$240.15	$240.10
Purchase #3	$103.25	3.612%	$106.9794	$106.98	$107.00	$107.00
Purchase #4	$126.44	4.327%	$131.9111	$131.91	$131.90	$131.90
Purchase #5	$116.53	12.404%	$130.9844	$130.98	$131.00	$131.00
Purchase #6	$28.88	11.801%	$32.2881	$32.29	$32.30	$32.30
Purchase #7	$187.47	13.129%	$212.0829	$212.08	$212.10	$212.10
7 purchase totals =	$851.30		$937.2646	$937.26	$937.30	$937.30