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	$25.67	3.273%	$26.5102	$26.51	$26.50	$26.50
Purchase #2	$64.38	12.341%	$72.3251	$72.33	$72.35	$72.30
Purchase #3	$63.49	6.358%	$67.5267	$67.53	$67.55	$67.50
Purchase #4	$59.95	4.565%	$62.6867	$62.69	$62.70	$62.70
Purchase #5	$193.55	3.802%	$200.9088	$200.91	$200.90	$200.90
Purchase #6	$86.42	11.379%	$96.2537	$96.25	$96.25	$96.30
Purchase #7	$63.26	13.525%	$71.8159	$71.82	$71.80	$71.80
7 purchase totals =	$556.72		$598.0271	$598.04	$598.05	$598.00