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	$19.93	6.756%	$21.2765	$21.28	$21.30	$21.30
Purchase #2	$89.95	4.530%	$94.0247	$94.02	$94.00	$94.00
Purchase #3	$32.88	6.478%	$35.01	$35.01	$35.00	$35.00
Purchase #4	$69.82	8.304%	$75.6179	$75.62	$75.60	$75.60
Purchase #5	$102.66	6.297%	$109.1245	$109.12	$109.10	$109.10
Purchase #6	$119.35	9.427%	$130.6011	$130.60	$130.60	$130.60
Purchase #7	$42.46	10.483%	$46.9111	$46.91	$46.90	$46.90
7 purchase totals =	$477.05		$512.5658	$512.56	$512.50	$512.50