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	$47.31	6.832%	$50.5422	$50.54	$50.55	$50.50
Purchase #2	$171.71	9.229%	$187.5571	$187.56	$187.55	$187.60
Purchase #3	$128.75	3.496%	$133.2511	$133.25	$133.25	$133.30
Purchase #4	$144.80	5.495%	$152.7568	$152.76	$152.75	$152.80
Purchase #5	$142.86	3.405%	$147.7244	$147.72	$147.70	$147.70
Purchase #6	$91.80	5.605%	$96.9454	$96.95	$96.95	$96.90
Purchase #7	$150.72	3.616%	$156.17	$156.17	$156.15	$156.20
7 purchase totals =	$877.95		$924.9470	$924.95	$924.90	$925.00