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	$77.67	5.595%	$82.0156	$82.02	$82.00	$82.00
Purchase #2	$165.81	5.719%	$175.2927	$175.29	$175.30	$175.30
Purchase #3	$27.62	13.815%	$31.4357	$31.44	$31.45	$31.40
Purchase #4	$54.60	12.784%	$61.5801	$61.58	$61.60	$61.60
Purchase #5	$180.73	4.872%	$189.5352	$189.54	$189.55	$189.50
Purchase #6	$93.80	10.435%	$103.588	$103.59	$103.60	$103.60
Purchase #7	$130.58	12.565%	$146.9874	$146.99	$147.00	$147.00
7 purchase totals =	$730.81		$790.4347	$790.45	$790.50	$790.40