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	$213.29	6.842%	$227.8833	$227.88	$227.90	$227.90
Purchase #2	$211.93	4.819%	$222.1429	$222.14	$222.15	$222.10
Purchase #3	$132.31	8.614%	$143.7072	$143.71	$143.70	$143.70
Purchase #4	$82.84	9.137%	$90.4091	$90.41	$90.40	$90.40
Purchase #5	$28.40	3.727%	$29.4585	$29.46	$29.45	$29.50
Purchase #6	$171.52	7.351%	$184.1284	$184.13	$184.15	$184.10
Purchase #7	$250.61	7.123%	$268.461	$268.46	$268.45	$268.50
7 purchase totals =	$1,090.90		$1,166.1904	$1,166.19	$1,166.20	$1,166.20