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	$159.58	11.782%	$178.3817	$178.38	$178.40	$178.40
Purchase #2	$120.41	5.764%	$127.3504	$127.35	$127.35	$127.40
Purchase #3	$152.83	11.447%	$170.3245	$170.32	$170.30	$170.30
Purchase #4	$128.85	8.681%	$140.0355	$140.04	$140.05	$140.00
Purchase #5	$243.36	11.133%	$270.4533	$270.45	$270.45	$270.50
Purchase #6	$43.73	4.283%	$45.603	$45.60	$45.60	$45.60
Purchase #7	$83.71	6.122%	$88.8347	$88.83	$88.85	$88.80
7 purchase totals =	$932.47		$1,020.9831	$1,020.97	$1,021.00	$1,021.00