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	$82.33	10.446%	$90.9302	$90.93	$90.95	$90.90
Purchase #2	$90.67	11.543%	$101.136	$101.14	$101.15	$101.10
Purchase #3	$129.60	7.463%	$139.272	$139.27	$139.25	$139.30
Purchase #4	$46.27	8.637%	$50.2663	$50.27	$50.25	$50.30
Purchase #5	$31.25	6.665%	$33.3328	$33.33	$33.35	$33.30
Purchase #6	$115.79	4.249%	$120.7099	$120.71	$120.70	$120.70
Purchase #7	$139.99	13.654%	$159.1042	$159.10	$159.10	$159.10
7 purchase totals =	$635.90		$694.7514	$694.75	$694.75	$694.70