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	$90.40	11.171%	$100.4986	$100.50	$100.50	$100.50
Purchase #2	$86.34	11.281%	$96.08	$96.08	$96.10	$96.10
Purchase #3	$23.68	11.727%	$26.457	$26.46	$26.45	$26.50
Purchase #4	$104.98	4.734%	$109.9498	$109.95	$109.95	$109.90
Purchase #5	$147.47	11.565%	$164.5249	$164.52	$164.50	$164.50
Purchase #6	$54.37	4.737%	$56.9455	$56.95	$56.95	$56.90
Purchase #7	$133.51	6.681%	$142.4298	$142.43	$142.45	$142.40
7 purchase totals =	$640.75		$696.8856	$696.89	$696.90	$696.80