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	$227.61	6.463%	$242.3204	$242.32	$242.30	$242.30
Purchase #2	$233.59	13.650%	$265.475	$265.48	$265.50	$265.50
Purchase #3	$80.41	10.174%	$88.5909	$88.59	$88.60	$88.60
Purchase #4	$198.31	7.599%	$213.3796	$213.38	$213.40	$213.40
Purchase #5	$159.41	6.225%	$169.3333	$169.33	$169.35	$169.30
Purchase #6	$19.70	12.370%	$22.1369	$22.14	$22.15	$22.10
Purchase #7	$96.50	3.113%	$99.504	$99.50	$99.50	$99.50
7 purchase totals =	$1,015.53		$1,100.7401	$1,100.74	$1,100.80	$1,100.70