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	$19.30	12.816%	$21.7735	$21.77	$21.75	$21.80
Purchase #2	$207.25	8.835%	$225.5605	$225.56	$225.55	$225.60
Purchase #3	$79.38	3.498%	$82.1567	$82.16	$82.15	$82.20
Purchase #4	$167.64	10.596%	$185.4031	$185.40	$185.40	$185.40
Purchase #5	$60.92	8.142%	$65.8801	$65.88	$65.90	$65.90
Purchase #6	$35.61	8.502%	$38.6376	$38.64	$38.65	$38.60
Purchase #7	$82.77	11.151%	$91.9997	$92.00	$92.00	$92.00
7 purchase totals =	$652.87		$711.4112	$711.41	$711.40	$711.50