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	$81.83	7.557%	$88.0139	$88.01	$88.00	$88.00
Purchase #2	$185.79	13.508%	$210.8865	$210.89	$210.90	$210.90
Purchase #3	$241.77	11.742%	$270.1586	$270.16	$270.15	$270.20
Purchase #4	$92.77	11.615%	$103.5452	$103.55	$103.55	$103.50
Purchase #5	$223.39	3.309%	$230.782	$230.78	$230.80	$230.80
Purchase #6	$41.43	9.411%	$45.329	$45.33	$45.35	$45.30
Purchase #7	$225.25	7.659%	$242.5019	$242.50	$242.50	$242.50
7 purchase totals =	$1,092.23		$1,191.2171	$1,191.22	$1,191.25	$1,191.20