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	$35.77	12.855%	$40.3682	$40.37	$40.35	$40.40
Purchase #2	$237.91	10.390%	$262.6288	$262.63	$262.65	$262.60
Purchase #3	$209.26	11.141%	$232.5737	$232.57	$232.55	$232.60
Purchase #4	$193.71	8.581%	$210.3323	$210.33	$210.35	$210.30
Purchase #5	$77.96	6.240%	$82.8247	$82.82	$82.80	$82.80
Purchase #6	$117.99	7.653%	$127.0198	$127.02	$127.00	$127.00
Purchase #7	$70.58	13.566%	$80.1549	$80.15	$80.15	$80.20
7 purchase totals =	$943.18		$1,035.9024	$1,035.89	$1,035.85	$1,035.90