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	$98.38	4.393%	$102.7018	$102.70	$102.70	$102.70
Purchase #2	$40.46	5.540%	$42.7015	$42.70	$42.70	$42.70
Purchase #3	$129.43	5.473%	$136.5137	$136.51	$136.50	$136.50
Purchase #4	$17.48	4.666%	$18.2956	$18.30	$18.30	$18.30
Purchase #5	$94.52	4.754%	$99.0135	$99.01	$99.00	$99.00
Purchase #6	$37.76	9.625%	$41.3944	$41.39	$41.40	$41.40
Purchase #7	$117.27	8.630%	$127.3904	$127.39	$127.40	$127.40
7 purchase totals =	$535.30		$568.0109	$568.00	$568.00	$568.00