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	$104.33	7.143%	$111.7823	$111.78	$111.80	$111.80
Purchase #2	$208.95	4.276%	$217.8847	$217.88	$217.90	$217.90
Purchase #3	$97.38	10.199%	$107.3118	$107.31	$107.30	$107.30
Purchase #4	$159.93	8.267%	$173.1514	$173.15	$173.15	$173.20
Purchase #5	$38.36	3.785%	$39.8119	$39.81	$39.80	$39.80
Purchase #6	$217.98	3.231%	$225.0229	$225.02	$225.00	$225.00
Purchase #7	$176.48	5.320%	$185.8687	$185.87	$185.85	$185.90
7 purchase totals =	$1,003.41		$1,060.8337	$1,060.82	$1,060.80	$1,060.90