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	$199.86	6.712%	$213.2746	$213.27	$213.25	$213.30
Purchase #2	$89.83	4.370%	$93.7556	$93.76	$93.75	$93.80
Purchase #3	$106.34	4.457%	$111.0796	$111.08	$111.10	$111.10
Purchase #4	$164.84	12.789%	$185.9214	$185.92	$185.90	$185.90
Purchase #5	$99.43	11.708%	$111.0713	$111.07	$111.05	$111.10
Purchase #6	$51.83	10.729%	$57.3908	$57.39	$57.40	$57.40
Purchase #7	$140.46	10.390%	$155.0538	$155.05	$155.05	$155.10
7 purchase totals =	$852.59		$927.5471	$927.54	$927.50	$927.70