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	$173.38	9.277%	$189.4645	$189.46	$189.45	$189.50
Purchase #2	$84.88	5.374%	$89.4415	$89.44	$89.45	$89.40
Purchase #3	$204.56	11.133%	$227.3337	$227.33	$227.35	$227.30
Purchase #4	$157.55	9.687%	$172.8119	$172.81	$172.80	$172.80
Purchase #5	$35.52	12.667%	$40.0193	$40.02	$40.00	$40.00
Purchase #6	$65.57	10.678%	$72.5716	$72.57	$72.55	$72.60
Purchase #7	$76.84	8.227%	$83.1616	$83.16	$83.15	$83.20
7 purchase totals =	$798.30		$874.8041	$874.79	$874.75	$874.80