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	$123.73	13.185%	$140.0438	$140.04	$140.05	$140.00
Purchase #2	$101.71	9.664%	$111.5393	$111.54	$111.55	$111.50
Purchase #3	$24.81	12.522%	$27.9167	$27.92	$27.90	$27.90
Purchase #4	$211.33	3.798%	$219.3563	$219.36	$219.35	$219.40
Purchase #5	$236.90	8.552%	$257.1597	$257.16	$257.15	$257.20
Purchase #6	$223.77	10.629%	$247.5545	$247.55	$247.55	$247.60
Purchase #7	$58.63	6.531%	$62.4591	$62.46	$62.45	$62.50
7 purchase totals =	$980.88		$1,066.0294	$1,066.03	$1,066.00	$1,066.10