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	$118.29	10.717%	$130.9671	$130.97	$130.95	$131.00
Purchase #2	$210.96	13.822%	$240.1189	$240.12	$240.10	$240.10
Purchase #3	$40.46	13.330%	$45.8533	$45.85	$45.85	$45.90
Purchase #4	$46.36	4.389%	$48.3947	$48.39	$48.40	$48.40
Purchase #5	$55.25	12.127%	$61.9502	$61.95	$61.95	$62.00
Purchase #6	$89.54	11.202%	$99.5703	$99.57	$99.55	$99.60
Purchase #7	$170.62	7.308%	$183.0889	$183.09	$183.10	$183.10
7 purchase totals =	$731.48		$809.9434	$809.94	$809.90	$810.10