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	$77.54	3.391%	$80.1694	$80.17	$80.15	$80.20
Purchase #2	$197.90	9.865%	$217.4228	$217.42	$217.40	$217.40
Purchase #3	$189.73	10.823%	$210.2645	$210.26	$210.25	$210.30
Purchase #4	$100.26	3.403%	$103.6718	$103.67	$103.65	$103.70
Purchase #5	$88.76	7.502%	$95.4188	$95.42	$95.40	$95.40
Purchase #6	$102.79	8.317%	$111.339	$111.34	$111.35	$111.30
Purchase #7	$7.28	7.365%	$7.8162	$7.82	$7.80	$7.80
7 purchase totals =	$764.26		$826.1025	$826.10	$826.00	$826.10