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	$143.27	6.505%	$152.5897	$152.59	$152.60	$152.60
Purchase #2	$223.44	3.784%	$231.895	$231.90	$231.90	$231.90
Purchase #3	$32.29	8.534%	$35.0456	$35.05	$35.05	$35.00
Purchase #4	$231.85	9.336%	$253.4955	$253.50	$253.50	$253.50
Purchase #5	$16.27	12.564%	$18.3142	$18.31	$18.30	$18.30
Purchase #6	$73.82	7.464%	$79.3299	$79.33	$79.35	$79.30
Purchase #7	$46.31	9.666%	$50.7863	$50.79	$50.80	$50.80
7 purchase totals =	$767.25		$821.4562	$821.47	$821.50	$821.40