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	$17.39	10.119%	$19.1497	$19.15	$19.15	$19.10
Purchase #2	$121.79	4.792%	$127.6262	$127.63	$127.65	$127.60
Purchase #3	$188.81	11.666%	$210.8366	$210.84	$210.85	$210.80
Purchase #4	$110.90	12.299%	$124.5396	$124.54	$124.55	$124.50
Purchase #5	$78.84	4.832%	$82.6495	$82.65	$82.65	$82.60
Purchase #6	$6.71	6.721%	$7.161	$7.16	$7.15	$7.20
Purchase #7	$99.69	6.668%	$106.3373	$106.34	$106.35	$106.30
7 purchase totals =	$624.13		$678.2999	$678.31	$678.35	$678.10