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	$23.37	10.769%	$25.8867	$25.89	$25.90	$25.90
Purchase #2	$197.34	7.813%	$212.7582	$212.76	$212.75	$212.80
Purchase #3	$48.56	4.593%	$50.7904	$50.79	$50.80	$50.80
Purchase #4	$42.37	13.537%	$48.1056	$48.11	$48.10	$48.10
Purchase #5	$48.44	10.478%	$53.5155	$53.52	$53.50	$53.50
Purchase #6	$178.53	12.240%	$200.3821	$200.38	$200.40	$200.40
Purchase #7	$47.52	10.496%	$52.5077	$52.51	$52.50	$52.50
7 purchase totals =	$586.13		$643.9462	$643.96	$643.95	$644.00