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	$128.82	8.518%	$139.7929	$139.79	$139.80	$139.80
Purchase #2	$88.71	5.390%	$93.4915	$93.49	$93.50	$93.50
Purchase #3	$102.78	8.853%	$111.8791	$111.88	$111.90	$111.90
Purchase #4	$71.31	8.442%	$77.33	$77.33	$77.35	$77.30
Purchase #5	$173.42	5.186%	$182.4136	$182.41	$182.40	$182.40
Purchase #6	$75.36	10.251%	$83.0852	$83.09	$83.10	$83.10
Purchase #7	$175.98	8.285%	$190.5599	$190.56	$190.55	$190.60
7 purchase totals =	$816.38		$878.5522	$878.55	$878.60	$878.60