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	$154.65	6.197%	$164.2337	$164.23	$164.25	$164.20
Purchase #2	$64.42	7.230%	$69.0776	$69.08	$69.10	$69.10
Purchase #3	$152.47	8.231%	$165.0198	$165.02	$165.00	$165.00
Purchase #4	$162.96	11.565%	$181.8063	$181.81	$181.80	$181.80
Purchase #5	$30.50	3.736%	$31.6395	$31.64	$31.65	$31.60
Purchase #6	$95.61	10.753%	$105.8909	$105.89	$105.90	$105.90
Purchase #7	$34.62	3.714%	$35.9058	$35.91	$35.90	$35.90
7 purchase totals =	$695.23		$753.5736	$753.58	$753.60	$753.50