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	$76.89	6.217%	$81.6703	$81.67	$81.65	$81.70
Purchase #2	$94.50	8.598%	$102.6251	$102.63	$102.65	$102.60
Purchase #3	$165.27	12.376%	$185.7238	$185.72	$185.70	$185.70
Purchase #4	$176.41	5.133%	$185.4651	$185.47	$185.45	$185.50
Purchase #5	$64.41	12.226%	$72.2848	$72.28	$72.30	$72.30
Purchase #6	$245.28	13.453%	$278.2775	$278.28	$278.30	$278.30
Purchase #7	$41.39	6.290%	$43.9934	$43.99	$44.00	$44.00
7 purchase totals =	$864.15		$950.0400	$950.04	$950.05	$950.10