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	$18.28	13.785%	$20.7999	$20.80	$20.80	$20.80
Purchase #2	$101.45	10.156%	$111.7533	$111.75	$111.75	$111.80
Purchase #3	$128.56	9.164%	$140.3412	$140.34	$140.35	$140.30
Purchase #4	$110.39	13.682%	$125.4936	$125.49	$125.50	$125.50
Purchase #5	$248.44	4.478%	$259.5651	$259.57	$259.55	$259.60
Purchase #6	$173.31	9.531%	$189.8282	$189.83	$189.85	$189.80
Purchase #7	$159.37	6.231%	$169.3003	$169.30	$169.30	$169.30
7 purchase totals =	$939.80		$1,017.0816	$1,017.08	$1,017.10	$1,017.10